United States
Environmental Protection
Agency
Office of
Drinking Water
Washington, D C 20460
EPA-570/9-79-019
Water
&EPA
Viruses, Organics, and Other
Health-Related Constituents
of the Occoquan Watershed
and Water Service Area
Part I: Trihalomethanes,
Pesticides, and Metals
September 1979
WASHINGTON, D.C.
•
V.
\
OCCOQUAN
WATERSHED
MARYLAND
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EPA 570/9-79-019
VIRUSES, ORGANICS, AND OTHER HEALTH-RELATED
CONSTITUENTS OF THE OCCOQUAN WATERSHED
AND WATER-SERVICE AREA
PART I: TRIHALOMETHANES, PESTICIDES, AND METALS
by
Robert C. Hoehn and Clifford W. Randall
Department of Civil Engineering
Virginia Polytechnic Institute and State University
Blacksburg, Virginia 24061
Project No. 68-01-3202
Project Officer
Frank A. Bell, Jr.
Office of Drinking Water
Washington, D.C. 20460
Criteria and Standards Division
Office of Drinking Water
U.S. Environmental Protection Agency
Washington, D.C. 20460
September, 1979
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CONTENTS
Foreword v
Preface vi
Executive Summary vil
Figures x
Tables xi
Abbreviations and Symbols xiv
Acknowledgments ' xv
1. Introduction 1
General Description of the Study 1
Background Information 3
The Watershed 3
The Sampling Sites 3
Description of FCWA's Water Treatment Facilities 8
Characteristics of Raw and Finished Water 8
References 12
2. Conclusions 13
3. Recommendations 16
4. Materials and Methods 17
Heavy Metals 17
Pesticides 17
Volatile Organics 18
Supplemental Water Quality Data 20
References 21
5. Results and Discussion 22
Heavy Metals 22
Raw Water Concentrations 22
Finished Water Concentrations 22
Pesticides 26
Organochlorine Pesticides 26
Organophosphorus Insecticides 34
Chlorophenoxy Herbicides 34
Pesticides and Land Uses 37
ii
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Volatile Organics 37
Occoquan-I: 1975-1976
Frequency and Distribution 39
Comparison with Other Studies 49
Occoquan-II: 1976-1977 49
Frequency and Distribution
THM Concentrations in Dechlorinated Samples 52
Comparison with Other Studies 56
Total Organic Carbon 61
Comparison of Occoquan-I and II THM's 61
Data Selection for Determining an Average THM Concentration 65
Relationships Between THM's and Raw Water Quality 65
Theoretical Considerations 65
Analytical Approach 67
Correlations Between TTHM's and Other Data 69
Results of Multiple Regression Analysis 72
Relationships to Algae Growth 72
Special Studies 74
THM Concentration Variations with Time of Flow From Tap. 74
Haloforms in Filter Back-Wash Water 74
References 78
Supplemental Data 80
Appendices
A. Heavy Metals at Sites A through F for the Period June, 1975 -
May, 1976 81
B. Pesticide Concentrations at Sites A through F for the Period
June'- November, 1975 , 92
C. Volatile Organics Concentrations at Sites A-F, Occoquan-I and
Sites C-G, Occoquan-II 107
D. Supplemental Data 133
E. Results of the Multiple Regression Analysis of Raw Water
Characteristics and Trihalomethane Concentrations 163
iii
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DISCLAIMER
This report has been reviewed by the Office of Drinking Water, U. S.
Environmental Protection Agency, and approved for publication. Approval does
not signify that the contents necessarily reflect the views and policies of
the U.S. Environmental Protection Agency, nor does mention of trade names or
commercial products constitute endorsement or recommendation for use.
IV
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FOREWORD
The Office of Drinking Water has broad interests in all aspects of
rendering a safe drinking water for the American public. .These interests
run from questions of wastewater and urban impacts on raw water quality to
the effects of treatment and the quality of distributed water.
The part of the "Occoquan" project reported herein addresses this
broad range of interests with respect to trihalomethanes, pesticides, and
metals, in detail and depth, with respect to a single, urbanizing reservoir
and water service area. This project should assist engineers and scientists
to understand system variations and thereby better interpret results from
national studies based on limited sampling from a number of systems. It
also supplies indications and directions that should be investigated and
considered in planning further studies or details for regulations imple-
mentation. It will also provide a "fix" in time for raw and finished
water quality for comparison with environmental measurements made in future
times as urbanization continues and advanced waste treatment changes are
implemented.
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PREFACE
The project discussed in this report was begun soon after the passage of
the Safe Drinking Water Act in 1974 (P.L. 93-523) and the.completion of the
EPA's National Organics Reconnaissance Survey (NORS) involving 80 cities in
the United States. Late in 1974, the public began to be made aware that
drinking water supplies, though microbiologically safe, may be contaminated
with hazardous organic chemicals contributed by industries and created during
the disinfection process. Extensive coverage by the news media fostered
public interest in the subject, and because the data base was so limited at
the time, EPA immediately responded by conducting in-house and extra-mural
research to determine the extent of the problem and how best to solve it.
Since then, much has been accomplished.
This project, referred to as the Occoquan Project, carried out in cooper-
ation with the Fairfax County Water Authority, was conceived initially as an
opportunity to study extensively a water system that serves a large population
(approximately 640,000) in a rapidly urbanizing area of northern Virginia.
The variations in concentrations of heavy metals, pesticides, and selected
volatile organics (especially the trihalomethanes) were of special interest,
so provisions were made to sample at several intervals during all seasons for
two years. The project is truly unique in that, to date, more data concern-
ing both raw- and finished-water concentrations of toxic substances and other
water-quality data, exists for FCWA's system than for any other in the
United States.
The site for this project was especially attractive because there was an
ongoing monitoring program (the Occoquan Watershed Monitoring Program, OWMP)
to provide weekly water quality data for the Occoquan Reservoir and its tri-
butaries which could be used in studies of possible correlations between raw-
and finished-water quality. Too, during the period of this project an advanced
waste treatment (AWT) facility was under construction which would effectively
remove pollutants contributed to the reservoir by the discharge of approxi-
mately six million gallons per day of secondary treated sewage to Bull Run,
one of the major tributaries. The Occoquan Project enabled an expansion of
the monitoring effort of the OWMP to include organics, heavy metals, and
viruses as part of the preconstruction data base. The AWT plant, owned and
operated by the Upper Occoquan Sewage Authority went on-line in late June,
1978, approximately one year after the monitoring provided for by this
contract was completed.
The Occoquan Project discussed in this report involved sampling the
reservoir, a major tributary, and several sites in the distribution system.
In addition to the monitoring for toxic substances, this project provided
for extensive virus monitoring and studies relating to virus-monitoring
methodology, but the latter will be covered in Part II of this report.
vi
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EXECUTIVE SUMMARY
In 1975, a study was initiated in the Occoquan (Virginia) watershed
and the water-service area of the Fairfax County Water Authority (FCWA) to
monitor both treated and untreated water for a variety of pesticides,
toxic heavy metals, and selected volatile organics, particularly those
known to be produced by chlorination during water-treatment processes.
Of particular interest were 1) the relative magnitudes of pesticide and
heavy metal concentrations in treated and untreated waters, 2) the extent
of contribution of these hazardous substances from the watershed, 3) the
concentration levels of trihalomethanes (THM's) in the finished waters
at the water treatment plant and at points distant in the distribution
system, and, finally, 4) the concentration variations that might be
attributable to seasonal changes or discernible differences in raw- or
finished-water characteristics. The project was adjunctive to the Occoquan
Watershed Monitoring Program, an ongoing project administered by Virginia
Polytechnic Institute and State University under the auspices of the
Virginia State Water Control Board. Financing for the monitoring program
is supplied by political subdivisions in northern Virginia that lie within
the Occoquan Watershed.
The project continued for two years— from June, 1975 through May,
1977— but pesticides and heavy metals were monitored only during the first
year of the project (Occoquan-I). During Occoquan-I, sampling sites were
established 1) on Bull Run, a major tributary to the Occoquan Reservoir,
both upstream and downstream of eleven sewage treatment plant discharges;
2) at the raw-water intake of FCWA's water-treatment facilities; 3) at a
point in the plant after treatment was complete, and 4) at two sites in the
distribution system, one in Alexandria, Virginia and the other in Fairfax
County. An open storage reservoir was located between the Alexandria site
and FCWA's treatment plant, and this reservoir is filled during the day
when the demand is low. In late afternoon and at night, the water from
the reservoir is rechlorinated at Cameron Station and used to supplement the
flow from FCWA's treatment facilities. During the second year of the study
(Occoquan-II), only volatile organics were monitored but a third, distant
site in the distribution system (at Dumfries, Virginia) was added.
During Occoquan-I, heavy metals (12 in all) were monitored monthly
at all sites, daily during one week in September, 1975, and bihourly on
one day (September 11) during that week. Pesticides (10 organochlorine
types, 4 organophosphorus-types, and 4 chlorophenoxy herbicides) were moni-
tored with about the same frequency as metals, but more emphasis was given
to the organochlorine types. They were monitored weekly for 18 weeks from
June into October, 1975. Volatile organics; including the THM's, carbon
tetrachloride (CCl^) and 1, 2-dichloroethane (DCE); were monitored with the
same frequency as the organochlorine pesticides. During Occoquan-II,
vii
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volatile organics were analyzed monthly at FCWA's raw water intake, at the
treatment plant after treatment was complete, and at the three distribution
system sites. Twice—during August, 1976 and March, 1977—each site in
the distribution system was monitored for THM's on five consecutive days.
Two additional features characterized the THM-analysis program during
Occoquan-II; 1) duplicate samples were collected and one was dechlorinated
to stop the haloform reaction and 2) the total organic carbon (TOC) con-
centrations were determined.
During both years of the Occoquan project, supplemental studies were
conducted periodically to provide additional data concerning factors that
affect the haloform reaction. In addition, during both years of the study,
supporting data—pH, temperature, chlorine concentrations, etc.—were
recorded each time a sample of raw or finished water was collected for
analysis.
An additional feature of this project was that an attempt was made to
determine, statistically, whether any relationship could be demonstrated
between raw water quality and concentrations of THM's in the finished
water. A good fit of the data was obtained by multiple regression analyses
with several water-quality parameters that reflected the extent of runoff
to the reservoir and algae growth within the reservoir. Unfortunately, the
equations were not "models," in the sense that they were not predictive,
and a much larger data base is required to develop true models. During
Occoquan-II, a severe drought occurred, and the water quality at the dam
site improved considerably. There was also a commensurate decline in the
finished-water THM concentrations, so, while the correlations between water
quality and THM's could not be statistically validated because there were
insufficient data, one can intuitively suspect that a strong causal rela-
tionship exists between THM's, runoff, and algae growth.
The heavy metal concentrations in finished water were routinely low
except in three instances: twice involving lead and once involving mercury.
These concentrations were not found in subsequent samples and,
thus, did not cause a violation of the Primary Drinking Water Maximum Con-
taminant Level (MCL). Secondary limits (aesthetic limits) for copper, iron,
and manganese were exceeded in drinking water collected at the treatment
plant but may have reflected corrosion effects from long-standing water in
the feeder pipe. No limits were exceeded in other distribution-system
samples, indicating minimal aesthetic effects.
Very low quantities of organochlorine pesticides and chlorophenoxy herbi-
cides were detected on numerous occasions in drinking water and, in each
instance where an MCL has been established by the Environmental Protection
Agency, the concentrations were far below the established limit.
The terminal TTHM concentrations (those attained after reaction to com-
pletion under given conditions of available precursors and chlorine) of the
individual samples were greater than 100 Mg/l 98 percent of the time during
Occoquan-I and 85 percent of the time during Occoquan-II. Dechlorinated
samples for THM analysis were collected only during Occoquan-II and exceeded
100 yg/1 62 percent of the time. (Trihalomethane regulations proposed by the
viii
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Environmental Protection Agency show a limit for TTHM of 100 yg/1 based on an
annual average in dechlorinated samples). In addition, there were distinct
seasonal variations in THM concentrations during both years, but the highest
concentrations were observed during different months—in July of 1975 and in
October of 1976. Chloroform accounted for approximately 90 percent of the
total THM (TTHM) concentrations, and dichlorobromomethane accounted either for
all or most of the remaining 10 percent on most occasions. TTHM concentrations
during Occoquan-I and Occoquan-II were, respectively: means, 249 and 173 yg/1;
medians, 238 and 164 yg/1; and ranges, 40-531 and 43-889 Pg/1.
There were distinct seasonal differences not reflected in the statistics
just cited, a fact already alluded to, and the variability of the observed
THM concentrations was quite high, even when sampling was frequent. The
standard deviations, expressed as percents of the means, for the various
sampling frequencies during the two-year study were: bihourly, 11 percent;
daily, 28 percent; weekly, 30 percent; and monthly, 36 percent. Seasonally,
the lowest variations in 1975-1976 were observed during the period of March
through May, and in 1976-1977, during December through February.
Trihalomethane concentrations in dechlorinated samples, expressed as a
percentage of the terminal concentrations, were lower in the winter than during
the summer (45 vs. 72 percent, respectively). There appeared to be a reason-
ably good linear correlation (R=0.74) between the water temperatures and the
CHC1_ concentrations in dechlorinated samples when the concentrations were ex-
pressed as a percentage of that in non-dechlorinated samples. The relationship
between temperature and the CHC1, concentrations themselves was poor.
To illustrate the potential variability of annual averages caused by a
particular sampling pattern, mean TTHM's (dechlorinated samples), were computed
for three combinations of monthly analytical results: 1) January, April, July,
and October; 2) February, May, October, and November; and 3) March, June,
September, and December. The means so computed varied considerably with a
maximum spread of 37 yg/1 between the high and low values. This demonstrates
the degree of variability which might be experienced in any given system.
Carbon tetrachloride (CC1.) appeared in 13 percent of the finished water
samples collected during Occoquan-II, in concentrations ranging from 1 to 7
yg/1. This compound is not a product of the reaction between chlorine and
organic compounds in raw water. The most likely source is from the chlorine
gas itself (CCl^ is a known contaminant of chlorine) because there are no
known industrial dischargers of CC1, to the Occoquan Reservoir, and none was
ever detected in the raw water.
This report was submitted in fulfillment of Contract No. 68-01-3202 by
the Research Division of Virginia Polytechnic Institute and State University
and its subcontractor, The Carborundum Company, under the sponsorship of the
U.S. Environmental Protection Agency. This report covers the period from
May 23, 1975 through May 31, 1977, and work was completed as of February 1,
1978.
ix
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FIGURES
Number Page
1 Map of northern Virginia showing the general location of the
Occoquan watershed 4
2 Occoquan watershed showing locations of sewage treatment plants
and sampling stations of the Occoquan Watershed Monitoring
Program 5
3 The Occoquan watershed showing five of the seven sampling
sites during the organics monitoring program 7
4 Distribution of TTHM concentrations observed in finished
water during 1975-1977 42
5 Weekly and daily variations in THM's during 1975 at FCWA's
water treatment plant and at two distribution system sites . . 45
6 Bihourly variations in THM's one day during 1975 at FCWA's
water treatment plant and two distribution system sites. ... 46
7 Variations in TTHM concentrations in finished water at the
water-treatment site, June, 1975-May, 1976 47
8 Variations in CHBrCl2 concentrations in finished water at the
water treatment site; June, 1975-May, 1976 48
9 Instantaneous TTHM concentrations in dechlorinated finished
water at four sites during Occoquan II 55
10 Relationship between finished-water temperatures and concen-
trations of THM's in dechlorinated samples, expressed as a
percentage of terminal THM concentrations 59
11 Relation between instantaneous TTHM concentrations and water
temperature at the treatment plant and three distribution
system sites 60
12 Annual mean TTHM concentrations in finished water (not dechlori-
nated) at the treatment plant and at sites in the distribution
system during Occoquan-I and Occoquan-II 64
13 Different "Annual Mean" TTHM concentrations made possible by
grouping the Occoquan-II data base in three different ways . . 66
14 Variations in TTHM concentration, chlorine dose, and chlorine
residuals in finished waters; June, 1975-May, 1976 71
15 Relationship between concentrations of chlorophyll-a in the
Occoquan Reservoir and finished-water TTHM concentration
during the summers of 1975 and 1976 73
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TABLES
Number Page
1 Listing of Health-Related Constituents Monitored in the Occoquan
Watershed and Water Service Area from June, 1975 through May, 1977 . . 2
2 Sampling Site Locations and Descriptions 6
3 Averages and Ranges of Finished Water Production Rates at Fairfax
County Water Authority During Project Period 9
4 Average Characteristics of Raw and Finished Water at the Fairfax
County Water Authority's New Lorton Treatment Facility During
Project Period, May 1975-May 1977 10
5 Statistical Evaluation of Monthly Variations Observed in Trace
Metals Consistently Present at Sites in the Occoquan Watershed
and Water Service Area, June, 1975-May, 1976 23
6 Statistical Evaluation of Daily Variations Observed in Trace
Metals Consistently Present at Sites in the Occoquan Watershed
and Water Service Area, June, 1975-May, 1976 .... 24
7 Statistical Evaluation of Bihourly Variations Observed in Trace
Metals Consistently Present in Untreated and Finished Water,
September 11, 1975 25
8 Finished Water (Sites D, E, and F) Concentrations of Trace Metals
for Which Secondary Standards are Proposed 27
9 Finished Water (Sites D, E, and F) Concentrations of Trace Metals
for Which There are Proposed Primary Standards, June, 1975
through May, 1976 28
10 Summary of Organochlorine Pesticide Occurrences in Untreated
Waters at Three Sites, June, 1975 - May, 1976 30
11 Summary of Organochlorine Pesticides Occurrences in Finished
Water, June, 1975 - May, 1976 31
12 Concentrations of Organochlorine Pesticides Observed in Spot
Samples Taken at the Fairfax County Water Authority's Water
Treatment Plant, September 11, 1975 33
xi
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Number Page
13 Organophosphorus Insecticide Analysis Frequency During June -
November, 1975 35
14 Summary of Herbicide Occurrences in Untreated Water at Three
Sites (A, B and C) and in Finished Water at the FCWA Water
Treatment Facility (Site D), June, 1975 - May, 1976. . . ' 36
15 A Comparison of Land Uses in the Two Sub-Basins of the Occoquan
Watershed 38
16 Frequency of Volatile Organics Greater than or Equal to One
Microgram per Liter at All Sampling Sites, June, 1975 - May,
1976 40
17 Chloroform Concentrations (Micrograms per liter), Variability, and
Frequency in Waters from Above and Below Sewage Treatment Plant
Discharges and in Raw and Treated Drinking Water from June, 1975
Through May, 1976 41
18 Variations in Total Trihalomethane (TTHM) Concentrations Observed
in Finished Drinking Water at Three Locations During the Period
From June, 1975 through May, 1976 44
19 Comparisons of Haloform Concentrations Observed During the NORS,
NOMS, and Occoquan-I Studies 50
20 Frequency of Volatile Organics Greater than or Equal to One Micro-
gram per Liter at All Sampling Sites, June, 1976 - May, 1977 51
21 Statistical Comparisons of Trihalomethane Concentrations in
Finished Water at FCWA's Treatment Plant and at Three Sites in
the Distribution System: May, 1976 - June, 1977 53
22 Comparisons Between Trihalomethane and Chlorine Concentrations
Observed at FCWA's Treatment Plant and at Three Sites in the
Distribution System: May, 1976 - June, 1977 54
23 Comparisons of Haloform Concentrations Observed During the NOMS
and Occoquan-II Studies 57
24 Comparisons of Haloform Concentrations in Dechlorinated Finished
Water Samples Collected During the NOMS and Occoquan-II Studies. ... 58
25 A Comparison of Total Trihalomethanes by Three Month Periods
During the Occoquan-I (1975-1976) and Occoquan-II (1976-1977)
Studies 63
26 Physical, Chemical, and Hydrological Factors That May Alter Raw
Water Quality and Subsequent Trihalomethane Concentrations in
Finished Drinking Water .- 68
xii
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Number Page
27 Results of Linear Least Squares Regression Analyses Between
Finished-Water Trihalomethane Concentrations and Raw Water
Quality 70
28 Analytical Data Derived From Experiments to Determine the Changes
in Haloform Concentrations at Various Intervals After Opening
Sampling Tap in Distribution System of the Fairfax County Water
Authority in Dumfries, Va., (Site G) 75
29 Analytical Data Collected During Special Studies to Determine
Terminal Haloform Concentrations in Finished Water Immediately
Preceding and Following Filter Backwash and in the Backwash
Itself 76
xiii
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LIST OF ABBREVIATIONS AND SYMBOLS
ABBREVIATIONS
CCE
CPH
DCE
FCWA
GAG
g/1
km
MCL
mg/1
MGD
ug/1
Uinol/1
ymhos/cm
NOMS
NORS
OCP
OPI
OWMP
THM
TTHM
TOC
UOSA
VO
VOA
VPI & SU
SYMBOLS
— Carbon Chloroform Extract
— Chlorophenoxy herbicides
— 1,2 - dichloroethane
— Fairfax County Water Authority
— granular activated carbon
— grams per liter
— kilometer
— maximum contaminant level
— milligrams per liter
— million gallons per day
— micrograms per liter
— micromoles per liter
— micromhos per centimeter
— National Organics Monitoring Survey
— National Organics Reconnaissance Survey
— organochlorine pesticides
— organophosphorus pesticides
— Occoquan Watershed Monitoring Program
— trihalomethanes
— total trihalomethanes
— total organic carbon
— Upper Occoquan Sewage Authority
— volatile organics
— volatile organics analysis
— Virginia Polytechnic Institute and State University
Ag -silver
As -arsenic
Ba -barium
Cd —cadmium
CHBrCl- -bromodichloromethane
CHBr^Cl -chlorodibromomethane
CHC1- -chloroform
CC1, -carbon tetrachloride
Cr
Cu
Fe
Hg
Mn
Pb
Se
Zn
-chromium
-copper
-iron
-mercury
-manganese
-lead
-selenium
-zinc
xiv
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ACKNOWLEDGMENTS
A special debt of gratitude is due the Fairfax County Water Authority
for making this project possible and for being willing to allow their water
system and operations to be scrutinized so thoroughly. Special thanks are
due Mr. Craig Cameron, the Laboratory Director at the treatment facilities,
for his interest and unwavering spirit of cooperation.
The authors wish to acknowledge also the subcontractors for this
project, The Carborundum Company, Niagara Falls, New York, for providing
the volatile organics analyses reported in this report. Special thanks
are extended to Dr. Paul Taylor, California Analytical Laboratories, Inc.,who
at the time of this project was president of the laboratories and a con-
sultant to The Carborundum Company, and to Dr. Peter T. B. Shaffer and
Mr. Robert A. Fluegge, who coordinated the handling and analyses of the
samples and also provided technical advice.
Special thanks are due the personnel of the Occoquan Watershed Moni-
toring Laboratory for their technical assistance, expecially Dr. Thomas J.
Grizzard, Director, and Ms. Kathleen Saunders, Research Associate. Ms.
Saunders had direct responsibility for collecting all samples and field
data and for carrying out the special studies described in this project.
Also, Mr. Richard Kotz, Department of Statistics, and Mr. Rodney Young,
Department of Biochemistry at VPI and SU are acknowledged for their efforts
in providing, respectively, the statistical modeling data and the pesticide
analyses presented in this report.
Finally, The Virginia-American Water Company (Alexandria, Virginia)
cooperated with the principals in this project by providing operational
data and advice regarding the sampling program. Their help greatly
facilitated the execution of this project and is gratefully acknowledged.
xv
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SECTION 1
INTRODUCTION
GENERAL DESCRIPTION OF THE STUDY
In June, 1975, an intensive monitoring effort, hereafter referred to
as the Occoquan Project, was begun in the Occoquan, Virginia, watershed and
water-service area of the Fairfax County Water Authority (FCWA). The
study, which began within six months after EPA's "eighty-city survey" (1)
and the enactment of the Safe Drinking Water Act (PL 93-523), was designed
to determine the concentration range and variability of a variety of
health-related constituents of both the treated water from the FCWA dis-
tribution system, which serves approximately 640,000 residents of several
northern Virginia communities, and the source water (the Occoquan Reservoir),
including one of its major tributaries (Bull Run). The constituents of
interest included: a variety of pesticides; haloforms (volatile organics,
principally the trihalomethanes); selected heavy metals, many of which are
toxic to humans; and certain viruses. The results of the virus monitoring
program and other related virus studies are presented in Part II of this
report.
The Occoquan Project was conducted by Virginia Polytechnic Institute
and State University (VPI&SU) and its subcontractor, The Carborundum Company,
as part of a larger, ongoing monitoring effort— the Occoquan Watershed
Monitoring Program (OWMP)— that is funded by the several political juris-
dictions that lie within the watershed and is conducted under the auspices
of the Virginia State Water Control Board. That program, begun in 1972,
is conducted by VPI&SU and provides weekly data concerning water quality
at several points within the Occoquan Reservoir and along its major tribu-
taries. The Occoquan Project provided for an expansion of the water-quality
data base compiled by the OWMP before an advanced waste treatment facility,
owned and operated by the Upper Occoquan Sewage Authority (UOSA), went
on-line in June, 1978. The OWMP, in addition to its routine monitoring, has
been the nucleus for several projects involving water-quality assessments,
urban runoff, and other related subjects. Reports of several of these
studies have appeared in the literature (2, 3, 4, 5).
This report contains a presentation and discussion of data collected
during the two-year study of health-related constituents that began in June,
1975. During the first year, chemical water constituents monitored at vary-
ing intervals included: six volatile, halogenated organics; ten organochlo-
rine pesticides; three chlorophenoxy herbicides; four organophosphorus insec-
ticides; and twelve heavy metals. (See Table 1). During the second year,
only the volatile, halogenated organics were monitored, and a third site in
the distribution system (in Dumfries, Virginia) was added. Provisions were
made for several, short-term studies with specific, well-defined objectives
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during both years of the study period. During both years of the study,
supplemental water-quality data were collected to aid in characterizing the
water when the constituents of major concern were monitored.
BACKGROUND INFORMATION
The Watershed
The watershed (area approximately 580 square miles), whose general loca-
tion is shown in Figure 1, consists of portions of four counties: Fairfax,
Fauquier, Loudoun, and Prince William. Two of the major tributaries join to
form the Occoquan Reservoir, which was impounded in 1957. At full pool, the
reservoir holds 9.8 billion gallons. The headwaters of the watershed are in
forested and agricultural areas. Cedar Run and Broad Run drain areas (approxi-
mately 340 square miles) that are almost entirely rural and undeveloped from
an urban perspective. On the other hand, Bull Run flows between and adjacent
to Fairfax County and the Manassas area, two of the most rapidly urbanizing
regions in the United States. Urban runoff and effluents from sewage treat-
ment plants [about 5.4 million gallons per day (MGD)] flow into Bull Run and
its tributaries, eventually reaching the reservoir. Construction of an
advanced wastewater treatment plant, under the auspices of the Upper Occoquan
Sewage Authority (UOSA), was completed during 1978, greatly reducing one
source of pollution in the reservoir. Figure 2 shows details of the water-
shed, including the location of sewage treatment plants and sampling stations
that are routinely monitored as part of the Occoquan Watershed Monitoring
Program. The urbanized areas, constituting approximately twenty percent of
the total watershed, are mainly along Bull Run•(bordering Manassas), along
Flat Branch (draining Manassas to Bull Run), and along Big Rocky Run (a
tributary to Cub Run).
The Sampling Sites
During the first year of the study, there were six sampling sites: two
on Bull Run upstream and downstream of major discharges of treated sewage and
urban runoff, two at the FCWA's Lorton Water Treatment Facility (both raw and
finished waters) located near the reservoir high dam, and two at distant
points in the distribution system. During the second year, a third site in
the distribution system was added, and most of the sampling that year did not
include the sites on Bull Run. A more detailed description of the sampling
sites is given in Table 2.
The particular location for Site F was selected originally because an
open-storage reservoir is located between it and the water treatment plant.
During the day, when the demand is low, the reservoir fills. Between 4:00
p.m. and midnight, when the demand is high, the reservoir is used to supple-
ment the flow from the FCWA plant. However, during this study, most all
samples were taken at times when there was no contribution from the open
reservoir.
Figure 3 shows the locations of Sites A-E, which were within the water-
shed. Sites F and G lay outside the watershed, E being approximately 14
miles (22.5 km) southeast of the center of Fairfax and 12.5 miles (20.2 km)
-------
LOUDOUN
COUNTY
DULLES
INTERNATIONAL
AIRPORT
WASHINGTON
D.C.
*' [ /
OCCQUAN
FAUQUIER
COUNTY
/ WATERSHED
MANASSAS
FAIRFAX
COUNTY
%.A\WARRENTON
\ PRlNCEvWILLlAM
SCALE IN KILOMETERS
Figure 1. Map showing general location of the Occoquan Watershed
in relation to Washington, D.C.
-------
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TABLE 2. OCCOQUAN PROJECT SAMPLING SITE LOCATIONS AND DESCRIPTIONS*
Site
Location
Conditions
**,
A On Bull Run, 23 miles upstream of the con-
fluence of Bull Run and Occoquan Creek.
Site is designated "Catharpin" and is at
a point where Rt. 705 crosses Bull Run.
B On Bull Run, 3.1 miles below confluence
with Cub Run and 2.3 miles below the dis-
charge of the last of 11 sewage treatment
plants. The site is 14 miles below Site
A, approximately 9 miles above the con-
fluence of Bull Run and Occoquan Creek.
Approximately 1000 feet below the Occoquan
Reservoir dam from the raw water main to
the Fairfax County Water Authority's (FCWA)
water treatment plant. Samples were taken
from inside the "carbon house". The site
is approximately 18 miles from Site B and
9 miles from confluence of Bull Run and
Occoquan Creek.
Pump Station No. 2 of the Lorton High Ser-
vice Plant at FCWA water treatment plant.
Within the distribution system in Fairfax
County at the Fairfax County Storage Yard
on Hwy 29 near County Road 645.
The Prince Street Fire Station in Alexan-
dria, Va. At times, water from an open
storage reservoir is rechlorinated and
used to supplement flow from FCWA.
The Dumfries-Triangle Volunteer Fire De-
partment, Inc. 18329 Jefferson Davis
Highway.
Forested and agricultural
areas. Represents condi-
tions upstream of major
sewage treatment plants and
urban drainage.
Average flow approximately
75 cfs. Bull Run at this
point has received approxi-
mately 5.4 MGD of treated,
chlorinated sewage from 11
plants (6 from Prince Wil-
liam Co. and 5 from Fairfax
Co.) as well as urban and
agricultural drainage.
Raw water as received by the
Fairfax Co. Water Authori-
ty's (FCWA) three treatment
plants, combined capacity
approximately 60 MGD.
A mixture of finished waters
from the three treatment
plants of the FCWA.
Finished water approximately
10 hours distant from the
FCWA water treatment plants
at average flow.
Finished water approximately
8 hours distant from FCWA
water treatment plants at
average flow. The system
belongs to the Virginia
American Water Company.
Finished water approximately
13 hours distant from FCWA
water treatment plants at
average flow. The water going
to this site is derived totally
from the Occoquan Treatment
Plant.
*Site A is sampled routinely as part of the OWMP. The other sites listed are
separate from those sampled by OWMP personnel.
**This site was sold in February, 1978, and is no longer under FCWA's control.
-------
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7. There are distinct seasonal variations in the THM concentra-
tions in FCWA finished water, the highest appearing in the
early summer of 1975 but shifting to the early fall of 1976.
The lowest variations in 1975-1976 were observed during the
period from March through May (15 percent), and in 1976-1977,
during December through February (21 percent).
8. Instantaneous trihalomethane concentrations, expressed as
percents of the terminal concentrations at the consumer's tap,
were lower in the winter than in the summer (45 vs. 72 percent,
respectively). There appeared to be a reasonably good linear
correlation between water temperature and dechlorinated sample
CHC1 concentrations expressed as a percentage of the terminal
concentrations•
9. The variability of the TTHM concentrations markedly affected
the magnitude of several "annual averages" computed for three
combinations of monthly analytical results for 1976-77: 1)
January, April, July and October; 2) February, May, October
and November; and 3) March, June, September, and December.
The means for these three groups of data varied considerably
(105-142 ug/1 in dechlorinated samples) with a maximum spread
of 37 ug/1 between the high and low values. This demonstrates
the degree of variability which might be experienced in any
given system.
10. Detailed review of the relative THM data for the distribution
samples, as compared to each other and to the treatment plant
samples, indicates the following:
a. The THM concentrations in non-dechlorinated samples from
the treatment plant were about the same as those at the
distribution points during both 1975-76 and 1976-77.
This would seem to indicate that THM's in a single, non-
dechlorinated sample collected at the treatment plant
could be considered as representative of the entire
distribution system.
b. During 1976-77, the THM concentrations in the dechlori-
nated samples at the treatment plant and the two relatively
close distribution points were equivalent, but those at
the far-distant distribution site (Site G) were signifi-
cantly higher than at the treatment plant.
14
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c. A special study, twice repeated at Site G in June, 1977,
showed that initial samples had no detectable free-chlorine
residuals and very low THM concentrations but that subsequent
samples collected one and five minutes after the tap was
opened had both substantial levels of free chlorine and
THMs. This indicates that some process may be operating
to lessen THM concentrations in a distribution system,
and this possibilty merits further investigation.
d. Plots of data from analyses of weekly, daily and hourly
non-dechlorinated samples from the treatment plant and
two distribution points for four months in 1975 were
roughly comparable except at Site F in the evening and
during the night of September 11, 1975 (starting at 1600
hours). During this period, the THM concentrations at
Site F were significantly lower, a fact explainable by
pumpage from a supplemental storage reservoir (beginning
at 1600 hours) which would provide a water with a much
shorter exposure to chlorine and, consequently, lower
concentrations of THMs. These data emphasize the need
for precise observations of distribution conditions to
facilitate interpretation and understanding of water
quality variations.
11. Finished-water trihalomethane concentrations correlated well
with the variables that related to raw water chlorine demand
and to those related to runoff, e.g., rainfall and reservoir
elevation. Good fits of the data could be obtained by the
multiple regression analyses, but none of the regression
equations was a true model because none was predictive. There
was no consistent correlation between finished water THM
concentrations and total organic carbon concentrations in
either the untreated or finished water.
12. Reservoir algal densities (expressed as chlorophyll a) were
not included in the statistical analyses, but the available
evidence shows that the summertime algal chlorophyll a concentra-
tions in the Occoquan reservoir vary approximately linearly
with finished-water THM concentrations, strongly suggesting
that algae contribute significantly to the pool of THM precursor
organic compounds in that body of water.
13. Carbon tetrachloride (CC1 ) appeared in 13 percent of finished
water samples, during 1976-1977 in concentrations ranging from
1 to 7 ug/1. The most likely source is the chlorine used at
the water treatment plant. No CC1 was detected in raw water
during this period. During 1975-1976 CC1 and 1,2-dichloro-
ethane were not separately identified.
15
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SECTION 3
RECOMMENDATIONS
Five areas of additional study in connection with trihalomethanes are
recommended;
1. Additional efforts should be made to determine the relative impor-
tance of humates and algal metabolites as THM precursors in the Occoquan
Reservoir. If the algae prove to be significant contributors, as all the
available data indicate that they are, then increased attention to algal
growths near the raw water intake should be carefully monitored, especially
during the period from May through October, and appropriate control measures
instituted at the first indication of increased growth.
2. Additional studies should be conducted to determine whether the
FCWA distribution system may provide reactants or may by some other means
cause a reduction in THM concentrations when free chlorine is no longer
present. More attention should be given to distribution system conditions,
such as the presence of slimes or trapped air, which could promote either an
increase or a decrease in THM concentrations or reduce the free chlorine
residual to zero.
3. Some additional research should be conducted to determine if some
raw-water quality parameter could be used as an indicator of the need for
special treatment to minimize THM's.
4. Efforts should be made to determine the source(s) of CCl^ and DCE
that were measured in several finished-water samples. If these are contami-
nants of the chlorine gas used by FCWA, steps should be taken to minimize
them.
5. Consideration should be given to analyses of water for total
organic halogens (TOX) in order to obtain a more complete evaluation of
chlorine by-product concentrations than one has when only THM's are
monitored.
16
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SECTION 4
MATERIALS AND METHODS
HEAVY METALS
Samples for heavy metals were collected in acid-washed, glass jars
(approximately two liters) and preserved with nitric acid. Sufficient acid
was added to decrease the pH to 2.0 or less. The jars were then covered
with a thin, polyethylene film and sealed with a lid used for sealing jars
typically used for the home-canning of foods.
Analyses were conducted by atomic absorption spectroscopy with a Perkin-
Elmer Model 403 Atomic Absorption Spectrophotometer equipped with a deuterium
background corrector. Most metals were analyzed by direct aspiration of the
sample into the flame. However, when concentrations of some metals, princi-
pally lead, approached the detection limit, the samples were extracted with
methylisobutyl ketone (MIBK), according to procedures described by Mulford
(1), and the extracts were aspirated into the flame.
Arsenic and selenium were analyzed by the gaseous hydride method (2) and
mercury by a flameless procedure (3). These latter procedures permit detec-
tion at concentrations much lower than is possible by methods used for other
metals.
Standards were prepared daily by dilution of commerically available
stock solutions (Fisher Scientific Company) with a glass-distilled water that
had been passed through an anion-cation exchanger after distillation. At the
request of EPA, the laboratory at VPI&SU participated in a quality-assurance
program to verify the precision of the analytical procedures, and the results
were deemed satisfactory. The laboratory routinely participates in a similar
program by the United States Geological Survey.
PESTICIDES
Samples for pesticide analyses were collected in amber glass jugs that
held approximately four liters. They were transported to VPI&SU, usually
within no more than two weeks after collection, and were stored at approxi-
mately 4°C until they could be analyzed. No special precautions were taken
to preserve the samples because the pesticides of interest are slowly bio-
degradable.
The analyses were conducted according to procedures described in Appen-
dix A of the National Pollutant Discharge Elimination System discussion pre-
sented in the Federal Register (4). The procedures entailed extraction of
the samples with solvents (methylene chloride in hexane for the organophos-
phorus and organochlorine pesticides, and diethyl ether for the chlorinated
17
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phenoxy acids and their esters) and subsequent analysis by gas chromatography
(GC). Standards were obtained from the Environmental Protection Agency in
Cincinnati, Ohio, and the laboratory at VPI&SU that was responsible for the
analyses.
At the beginning of the study, EPA's Quality Assurance Branch submitted
pesticide samples (unknowns) to the analysts' laboratory (Department of Bio-
chemistry Pesticide and Organics Analysis Laboratory) to verify their ability
to detect the pesticides in question. The results were satisfactory. Rou-
tinely, as is accepted practice, the analysts spiked one water sample with
pesticides being analyzed and carried these samples through the entire analy-
tical scheme. This procedure was repeated each day analyses were performed.
The hexane extracts were passed through dry Florisil columns (6 g.) for
clean-up, and two fractions of the filtrate (the first and second 50-75 ml
portions) were analyzed for the pesticides. Typical recoveries were greater
than 90 percent in all instances.
During the analyses of both raw water and finished drinking water, many
unidentified peaks consistently appeared on the chromatograms. These were
noted but were not identified because such work was not required by the con-
tract. However, in several instances, pesticides required by the contract
which were identified in the samples by GC procedures were verified by mass
spectroscopy at VPI&SU.
VOLATILE ORGANICS
Sample collection procedures were the same during the two-year program,
but more attention was given to standardizing the sample-handling procedures
in the second year's effort. Details are given in the following sections.
Sample-Collection Procedures
Samples for volatile organics analyses (VOA) were collected in 50-ml,
glass bottles previously cleaned with detergent, distilled water, and ace-
tone, then heated at 550°C to combust any residual acetone and organic matter
not removed by the washing procedure. The sample bottles were filled to
overflowing, and a teflon disk was carefully positioned to avoid entrapment
of air in the bottle. Then, an aluminum cap was placed over the teflon liner
and firmly secured by crimping its edges with a commercially available crimp-
ing tool. The samples then were placed on wet ice and shipped by air express
to Sacramento, California, for analysis at the California Analytical Labora-
tories. During the second year, duplicate, finished-water samples were col-
lected and one was dechlorinated by adding sufficient potassium ferrocyanide
to reduce 10 mg/1 chlorine.
Sample Handling and Analysis Procedures
Sample Handling—
During the first year of the study, there were no specific instruction
given to the analysts regarding sample-handling procedures that should be
followed prior to the actual analyses because at that time not much was
known about the environmental variations that could affect the concentrations
18
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of volatile organics in sample.containers during storage. However, informa-
tion became available during the first year of study that showed storage con-
ditions and the time lapse before analysis possibly could affect the results,
so in the second year, detailed sample-handling procedures were specified as
part of the VOA protocol the analysts should observe. During the first year,
steps were taken to ensure that samples were not contaminated by haloforms
in the atmosphere. These steps included 1) removing all volatile organics
from the refrigerator used to store samples prior to their analysis and 2)
sealing of each sample in its own polyethylene bag. Later, it became known
that the time lapse between collection and analysis was important, so in the
second year of study, it was specified that samples should be analyzed no
sooner than seven days nor later than fifteen days after collection.
That year, the samples were placed on ice at the time of collection and
were shipped (usually the next day) to the analytical laboratory by air
express. The time in transit usually was one day, but never longer than two
days. Prior to analysis, the samples were left standing at ambient room
temperature (ca.22°-23°C) for a period not less than seven days and, as was
specified in the contract, the total elapsed time between sample collection
and analysis never exceeded fifteen days.
Sample Analysis—
All VGA's were by the Bellar-Lichtenberg procedure (5), a purge/trap
procedure wherein volatile organics are sparged with an inert gas (nitrogen
or helium) and adsorbed on a resin inside a "trap." The trap is then heated
rapidly and the desorbed VO gases are swept into the GC column. The detector
is a coulometric detector that"is particularly sensitive to halogenated
organics but not other types of "contaminating" organics.
During the study, personnel at the California Analytical Laboratories
and The Carborundum Company collaborated closely with Bellar and Lichtenberg
at EPA in Cincinnati to keep abreast of rapidly developing improvements. At
the beginning of the project, the analysts participated in a quality assur-
ance program with EPA in Cincinnati and proved themselves quite capable of
obtaining reliable data at the ug/1 level. Additional quality assurance
tests have been conducted by the California Department of Health, and there
is an established "internal" quality control program wherein at least one
sample in each set is spiked with several of the THM's. Typical recoveries
have been in the 90 to 100 percent range. The internal quality control
program was approved by both EPA and the California Department of Health.
Occasionally, though it was not specified in the contract to do so, the
volatile organics analyzed by gas chromatography were confirmed by mass spec-
troscopy. These confirmations were particularly useful in the first year of
the study to ensure the reliability of the analytical procedures for identi-
fying the specific volatile organics of concern and to eliminate the possi-
bility that other compounds with similar retention characteristics as the
volatile organics might be producing artifacts.
During the first year of the study, and through most of the second, the
particular GC column packing employed in the VOA procedure did not permit
19
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separation of 1,2-dichloroethane (DCE) and carbon tetrachloride (CCl^). In
February, 1977, a change was made in the type of packing, and for the remain-
der of the study, DCE and CCi^ were effectively separated during the analyses.
SUPPLEMENTAL WATER QUALITY DATA
Supplemental water quality data required by the contract included chlo-
rine residuals (free and total), pH, temperature, bacterial counts (coliforms
and total plate counts, the latter on finished water only), and notes concern-
ing any unusual characteristics such as high turbidity and any unusual color
or odor. All methods were according to Standard Methods For the Examination
of Water and Wastewater (6). During the second year, monitoring of finished
waters for total organic carbon (TOG) was required.
Chlorine Residuals
Both total and free residuals were determined by the DPD Ferrous Titri-
metric Method Sec. 409 E. The reliability to 0.1 mg/1 was verified by test-
ing aliquots of samples by the Amperometric Titration Method, Sec. 409 C.
The titrimetric method was suitable for analysis of all but the most turbid
samples, as are common to the tributary streams of the reservoir after a
rainstorm, but the residuals there were less than 0.1 mg/1 on all occasions.
The principal sites where chlorine residuals were important were those where
finished water samples were collected.
pH Value
The pH of all samples was determined according to Standard Methods Sec-
tion 424. A portable pH meter was used and standardized before each use with
commercially available buffer solutions.
Temperature
Temperature was measured according to Standard Methods Section 212 with
a mercury-filled Celsius thermometer calibrated in increments of 0.1 C. The
thermometer was placed in the sample immediately after collection and allowed
to equilibrate before the reading was taken.
Bacterial Counts
Coliforms—
The Multiple-Tube Fermentation Technique (Section 908) was used for both
total coliforms (908 A) and fecal coliforms (908 C). Both the presumptive
and confirmed tests were performed using five transplants of aliquots from
the serial dilutions. Occasionally, the completed test was performed to veri-
fy the identification reliability. Both raw and finished-water samples were
analyzed for coliforms, and the dilutions and media inoculations were per-
formed in the 'field. The tubes were returned to the laboratory for incuba-
tion within four to six hours.
20
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Total Plant Counts—
The standard plate count procedure (Section 907) was performed only on
finished waters. Plates were inoculated in the field at the time samples
were collected and returned to the laboratory for incubation within four to
six hours.
Total Organic Carbon (TOG)—
The TOC concentrations were determined (during Year 2) by analysis with
a Beckman Instruments 915A TOC Analyzer. Potassium phthalate standards
were used so that full-scale deflection on the strip chart recorder was
20 mg/1, and the reproductivity of analyses of standards was within 0.2
mg/1 of the true concentration. During the latter part of the study period,
the laboratory acquired a Dohrmann/Envirotech .Model 54 TOC Analyzer, permit-
ting analyses with precision to less than 50 yg/1 TOC.
REFERENCES
1. Mulford, C. E. Solvent Extraction Techniques for Atomic Absorption
Spectroscopy. Atomic Absorption Newsletter, 5_, 88-90, July-Aug. 1966.
2. Fernandez, F. J. Atomic Absorption Determination of Gaseous Hydrides
Utilizing Sodium Borohydride Reduction. Atomic Absorption Newsletter,
12 (4): 93-97, July-Aug. 1973.
3. The Perkin-Elmer Corporation. Instructions, Mercury Analysis System,
303-0832, 303-0830, Norwalk, Connecticut. October, 1972.
4. National Pollutant Discharge Elimination System, Appendix A, Federal
Register, 38, Part II, Sections 1, 2, and 7, November 28, 1973.
5. Bellar, T. A. and Lichtenberg, J. J. Determining Volatile Organics at
Microgram per-Litre Levels by Gas Chromatography. J. Am. Wtr. Wks.
Assoc. 66_ (12): 739-744, 1974. (Also in EPA-670/4-74-009, U. S. Environ-
mental Protection Agency, Cincinnati, Ohio, 1974, 28 pp.)
6. American Public Health Association, American Water Works Association,
and Water Pollution Control Federation. Standard Methods For the
Examination of Water and Wastewater, fourteenth edition. M.C. Rand,
A. E. Greenberg, M. J. Taras, and M. A. Franson, eds., American Public
Health Association, Washington, D.C. 1976. 1193 pp.
21
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SECTION 5
RESULTS AND DISCUSSION
HEAVY METALS
Of the 12 heavy metals that were monitored, only four— Cu, Fe, Mn, and
Zn— were present consistently at all six sampling sites. The average concen-
trations of these metals and their variations; observed in samples collected
monthly, daily, and blhourly; are shown, respectively, in Tables 5, 6, and 7.
Appendix A contains the individual data from which these tables (and others
to be presented later) were constructed.
Concentrations in Raw Water
The soils in the Occoquan Reservoir contain an abundance of Fe and Mn, a
fact reflected by the high concentrations in Bull Run at Sites A and B. At
the dam (Site C), concentrations of both these metals were considerably higher
than in Bull Run because the hypolimnetic waters in the reservoir either are
anaerobic or contain little oxygen (<10 percent saturation) during May through
September causing the Fe and Mn to exist in the reduced state, which makes
both metals more soluble than when they are oxidized. The FCWA aerates the
hypolimnion by forced-air injection through perforated tubing that extends
several hundred feet upstream from the dam. However, even this treatment does
not prevent the anaerobic sediments from releasing Fe(II) and Mn(II).
Both Cu and Zn appeared in relatively low concentrations in water from
Bull Run at Sites A and B even though Bull Run receives urban runoff that
normally contributes considerable quantities of Zn. Apparently, dilution and
removal by adsorption onto sediment are preventing water concentrations from
becoming high. Table 6 shows that Zn concentrations in raw water at the dam
site were lower than in Bull Run, most likely because Zn is removed by adsorp^
tion onto suspended solids that settle in the reservoir; however, Cu concen-
trations increased. The FCWA applies massive quantities of copper sulfate
(CuSO^) during May through October for algae control at several points in the
reservoir, including near the dam site, so it was not surprising that Cu
concentrations at Site C were greater than in Bull Run.
None of the other heavy metals (Ag, As, Ba, Cd, Cr, Hg, Pb, and Se) ever
appeared in significant concentrations in water at Sites A or B. At Site C
(the dam site), Ag, As, Cd, Cr, Hg, and Se seldom were observed; while Ba and
Pb appeared frequently in low concentrations.
Finished Water Concentrations
As might be expected, both Fe and Mn concentrations were reduced by
FCWA water treatment processes, though the average Fe concentration exceeded
22
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the water quality standard of 0.3 mg/1 at Site D. Apparently, iron precipi-
tated in the distribution system enroute to Sites E and F, because, as is
shown in Table 5, the average concentrations at these locations were nearly
an order of magnitude less than at the treatment plant. On the other hand,
concentrations of Cu and Zn were higher in finished water at all sites,
caused, no doubt, by contributions from the piping. It should be mentioned
that Fe, Mn, Cu, and Zn included in the proposed national standards are
secondary standards because those elements do not adversely affect human
health. Those proposed standards (Fe, 0.3 mg/1; Mn, 0.05 mg/1; Cu, 1.0 mg/1;
and Zn, 5.0 mg/1) are intended to ensure that both the aesthetic and organo-
leptic quality of the water supply are acceptable (1). At the time this
study was performed, the approval limits in force were those of the Virginia
State Health Department's Bureau of Sanitary Engineering, and these elements
were labeled "aesthetics." 'A statistical summary of the data for observed
Cu, Fe, Mn, and Zn concentrations is presented in Table 8. As can be seen,
the proposed national standards were seldom exceeded except that for Fe,
which was exceeded 14 percent of the time, most frequently at Site D.
Table 9 contains a synopsis of the finished water data concerning trace
metals for which MCL's in finished water are specified (2). Note that the
MCL for Pb was exceeded twice, both times at Site D when the observed concen-
trations were 100 and 80 ug/1. The mercury MCL was exceeded once, but since
it and lead were not found in subsequent samples, the proposed MCL's were
not considered to have been violated. It should be mentioned that lead was
never detected at Site A, only once at Site B, but eight times at Site C
(mean, 31.4 pg/1). The increase most likely can be explained by the fact
that the reservoir is located in a highly urbanized area and receives con-
siderable metal pollution from urban runoff and in rainfall (3,4). On the
dates when lead exceeded standards at Site D, the concentrations were zero
in the raw water. However, lead was detected approximately 30 percent of the
time (Table 9) in finished water. A Community Water Supply Study conducted
in 1969 (5) revealed that 1.4 percent of 969 water supplies contained lead
in excess of the MCL of 0.05 mg/1. It was mentioned that under certain
conditions, lead concentrations can become considerably high when water
stands overnight in lead pipes. Therefore, it is possible that lead is
being contributed by the piping at the treatment plants, but according to
a recent report of the National Research Council (NRC) of the National
Academy of Science (NAS) (6), lead can also be contributed during the treat-
ment of water, presumably as contaminants in the treatment chemicals as well
as from the hardware within the system itself. The report cited a study in
which metals concentrations in both raw and finished waters from 1577 systems
were compared. Higher mean concentrations of Fe, Zn, Pb, Cu and Al in finished
waters were evident from the five-year study conducted in the 1960's.
PESTICIDES
Organochlorine Pesticides (OCP)
All the OCP's are insecticides that can be grouped for discussion in
four categories. While an exhaustive review of the chemical and toxicologi-
cal information regarding these compounds is beyond the scope of this report,
a brief review of some pertinent facts will be helpful in interpretation of
the data obtained during the Occoquan study. For more detail, the interested
26
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reader is referred to the National Academy of Sciences (NAS) 1977 report
entitled "Drinking Water and Health" (6) from which the following facts
regarding the OCP's were obtained. Most concern regarding the environmental
impact of the OCP's centers about the facts that many of them are known or
suspected carcinogens, are extremely resistant to chemical or biological
decomposition, and tend to concentrate in organisms at successively higher
trophic levels in food chains.
Classes of OCP's—
The ten OCP's monitored in raw and finished water during the Occoquan
study fall into four distinctly different classes of organic compounds.
These are discussed briefly.
Cyclodienes— Six of the ten OCP's were in this group, all derivatives
of hexachlorocyclopentadiene. Included are: aldrin and dieldrin, which are
highly persistent and carcinogenic and which were banned October 1, 1974;
endrin; chlordane and heptachlor, which were suspended for use on agricul-
tural crops on April 1, 1976; and heptachlor epoxide. This group is regarded
by the NAS to be the most hazardous of all the residual pesticides in water.
The only one for which a MCL has been established is endrin (MCL: 0.2 ppb),
and that standards is based on chronic toxicity effects. An approval limit
of 0.5 ppb was in force during the period covered by this study.
Chlorinated Ethanes— Included are DDT, which was banned for all but
essential public health uses on January 1, 1973, and methoxychlor. DDT is
ubiquitous in the environment because it is highly persistent and bioconcen-
trates. DDE is-the principal breakdown product. The toxicity of DDT is
related to chronic effects, though there is also a definite carcinogenic
risk. There is no interim drinking water standard for DDT. The interim
standard for methoxychlor is 0.10 mg/1. It is not bioconcentrated and has
a low mammalian toxicity. During the project period, there were limits in
force of 0.05 mg/1 DDT and 0.10 mg/1, both specified in the Virginia Water
Works Regulations.
Hexachlorocyclohexanes— Lindane is the gamma isomer (one of eight) of
"benzene hexachloride" (BHC). (Commerical grade lindane is 99% pure gamma
isomer). An interim standard of 4 ppb has been established by EPA.
Camphene derivatives— Toxaphene is a complex mixture of at least 175
compounds, only 10 of which have been identified structurally. It is the
least understood of all the OCP's but apparently has not caused a great deal
of environmental harm. Residues are seldom detected on raw agricultural
products and, hence, toxaphene is not likely to appear in finished drinking
water.
Observed Concentrations of OCP's in the Occoquan Study—
Tables 10 and 11 present summaries of the observed occurrences of OCP's,
respectively, in raw and finished waters during the Occoquan study. As can
be seen from Table 10, three OCP's— DDT, dieldrin, and heptachlor epoxide—
were detected in raw water at one or more of the three locations at least
34 percent of the time. The para-para (p-p1) isomer of DDT is shown because
29
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it accounted for from 80 to 90 percent of the technical product used for
years. Its presence, in spite of the limited ban since 1973, attests to its
persistence in the environment. The high detection frequencies of dieldrin
and heptachlor epoxide and correspondingly low detection frequencies of
aldrin and heptachlor can be explained by the fact that dieldrin and hepta-
chlor epoxide are the major degradation products that persist after applica-
tion, respectively, of aldrin and heptachlor. Lindane was observed to be
present in more than 25 percent of the raw water samples.
The concentrations of the various OCP's in finished waters (Sites D,
E, and F), shown in Table 11, illustrate the persistence of DDT and hepta-
chlor epoxide through the treatment system. However, none of the existing
standards was ever exceeded. Methoxychlor appeared with approximately the
same frequency in finished water as in raw water (16 vs. 14 percent of the
time). Generally, but not always, the OCP's were observed most often at
Site D. The mean concentrations for DDT, heptachlor epoxide, methoxychlor
concentrations were, respectively, 39, 8.8, and 82.7 nanograms per liter.
Endrin was never observed in finished water and never was an established MCL
for any OCP exceeded. Appendix B, Tables B-l through B-6, contains the
results of the individual analyses for OCP's throughout the sampling period.
Note that those in eight of the samples were confirmed by mass spectroscopy.
Table 12 shows the concentrations of the OCP's recovered from selected
sites within FCWA's Lorton treatment facility and from the effluents of
three experimental granular activated carbon (GAG) filters that had been in
operation for approximately three months. While none of the MCL's were
exceeded, it is interesting to note that the concentrations of methoxychlor
in the GAG filter effluents were relatively high when compared to those in
water at various locations in the plant. Except for that in the effluent
from the 2 ft. WestVaCo WV-G Column (Site Z4), the concentrations of metho-
xychlor from the carbon columns approximated the mean concentration observed
in finished waters during the entire study period (Table 11). The WestVaCo
carbon's capacity for most of the pesticides appeared to have been exceeded
at the time of this particular sampling and, in fact, seemed to be desorbing
certain ones of the accumulated pesticides. The intent of the brief study
was to determine the pesticide removal effectiveness of various water treat-
ment processes, but the data are too few to substantiate any definite con-
clusions. A comparison with data in Appendix Table B-7 (bihourly analyses
on September 11, Site C) shows that OCP concentrations appeared to be reduced
through the treatment plant, but because there was no way to follow a slug
of water through the plant, no definite statement can be made concerning the
sequential removal by the various water treatment processes.
The OCP's were also monitored bihourly on September 11, 1975, at Sites
D, E, and F (finished waters). The results of the individual analyses
appear in Appendix B, Tables B-8 through B-10. Dieldrin, DDT, and hepta-
chlor epoxide appeared in a majority of the raw-water samples; while metho-
xychlor and aldrin, though present, appeared less frequently. During this
sampling period, only DDT and methoxychlor appeared in measurable concentra-
tions at Site D. Samples from Site E were relatively free of any OCP, and
none from Site F showed measurable concentrations of any OCP.
32
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33
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Organophosphorus Insecticides (OPI)
There are no interim primary standards (2) for any of the OPI's, but
four representatives of this class of pesticides were included in the first
year of the Occoquan monitoring study because the OPI's, as a class, are
widely used in the United States. Even though their effects on humans can be
quite severe (they inhibit proper nerve impulse transmission by inhibition
of cholinesterase),the OPI's are not as persistent in the environment as
the chlorinated pesticides and generally are not regarded as serious hazards
in water because they rapidly break down. (The interested reader is referred
to an EPA publication: "The Fate of Select Pesticides in the Aquatic Environ-
ment," Reference 7).
During 1975, a total of 48 raw-water samples and 34 finished-water
samples (Table 13) were analyzed for four OPI's: dimethoate, azodrin
(common name: monocrotophos), vapona (common names: DDVP and dichlorvous),
and ethion. Only once was any OPI detected (dimethoate, 0.068 Ug/1, at Site
A on August 26, 1975). There was concern that the prescribed analytical
procedure, involving a flame ionization detector, was not sensitive enough,
so all analyses were replicated using the 63}ji electron detector. Still no
OPI's were detected.
Chlorophenoxy Herbicides (CPH)
The herbicides are of importance in assessing water quality because they
are widely used to control aquatic and terrestrial weeds, and there is a
possibility that they may enter potable source waters. Two herbicides are
used extensively in the United States: 2,4-D (2,4-dichlorophenoxyacetic acid)
and 2,4,5-TP (Silvex) [2-(2,4,5-trichlorophenoxy) propionic acid]. A third,
2,4,5-T (2,4,5-trichlorophenoxyacetic acid), has been banned for major use
as an aquatic weed control chemical (2). The contract which provided for
the Occoquan study did not require that 2,4,5-T be analyzed, but because it
would appear during the gas chromatographic analysis for the other two, its
presence, if detected, was routinely reported. At the time of sampling, the
Virginia Water Works Regulations specified approval limits of 0.02 mg/1 for
2,4-D and 0.03 mg/1 for 2,4,5-TP. The interim primary drinking water
regulations (2) presently specify approval limits of 0.1 mg/1 and 0.01 mg/1
for 2,4-D and 2,4,5-TP, respectively, values that are 20 percent of the
assumed safe levels of these compounds in the total diet of animals. These
safe levels were derived from laboratory-determined dosages required to
induce toxic effects (both chronic and acute) in rodents and dogs.
Table 14 shows a statistical summary of the analytical results of the
CPH analyses. Even though the herbicides were detected in a majority of
both raw and finished water samples, the concentrations never even closely
approached the MCL's. (Individual data are in Appendix B, Tables B-ll
through B-14). It is interesting that 2,4,5-T, even though banned, did
appear in low concentrations four times in raw water samples and twice in
finished water.
34
-------
TABLE 13. ORGANOPHOSPHORUS INSECTICIDE ANALYSIS FREQUENCY
DURING JUNE - NOVEMBER, 1975
Sampling
Date
June
July
August
2
3
4
9
10
11
16
17
18
23
24
30
1
7
8
14
15
21
28
29
5
11
12
18
25
26
September 9
October
November
11
12
15
22
23
6
7
10
11
Sites
A
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
B
X
X
X
X
X
X
X
X
X
X
X
X
X
X
c
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
D E
X
X
X
X
X
X
X X
X X
X
X X
X X
X X
X X
X
X
X
X
X
X
F
X
X
X
X
X
X
X
X
35
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36
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Possible Relationships Between Pesticides Concentrations and Land Uses
in the Occoquan Watershed
It has been mentioned previously that no data are available that might
be used to predict the precise sources of pesticides found in the reservoir
and its tributaries, though it is probably true that runoff from both urban
and agricultural areas contribute the vast majority of the pesticides
detected. It should be emphasized that no samples were taken from the
Occoquan Creek tributary of the reservoir, and it is the one that drains
the largest land mass within the watershed. Table 15 was prepared to compare
the land uses in the two sub-basins of the Occoquan Watershed. The heaviest
pesticide applications, no doubt, would be in the tilled areas, which totalled
67.3 and 24.7 square miles, respectively, for the Occoquan Creek and Bull Run
Watersheds.
Examination of the individual pesticide concentration values in Appendix
B shows that pesticide concentrations generally increased downstream from
Site A to Site B in Bull Run. However, concentrations at the dam (Site C)
were often much higher, indicating that there were inputs from sources other
than Bull Run. For example, the mean concentrations and standard deviations
for DDT at Sites B and C were, respectively, 0.17 ± 0.5 yg/1 (16 samples) and
0.57 ± 1.0 yg/1 (11 samples). Most of the urban runoff entering the Occoquan
Reservoir has entered Bull Run upstream of Site B, and other than from some
slight agricultural activity along the northeast boundary of the reservoir,
there are no sources except Occoquan Creek for sizeable pollutant loads to
enter. These facts, considered along with data presented in Table 15 concern-
ing land use, lead . one to suspect that Occoquan Creek is a significant con-
tributor of the total pesticide load entering the Occoquan Reservoir. There
should be no real cause for concern regarding the safety of the water supply,
however, because no pesticide standard was exceeded during the study period.
VOLATILE ORGANICS
Volatile organics were monitored routinely for two years during the
Occoquan study, and, in addition, a number of short-term experiments were
conducted to contribute information regarding factors that influence haloform
production in water supplies. The routine monitoring effort during 1975 and
1976 (hereafter referred to as Occoquan-I) differed in several respects when
compared to the second year's study during 1976 and 1977 (hereafter referred
to as Occoquan-II).
The differences were as follows:
1. During Occoquan-I, the sampling frequency was greater during the
summer and fall.
2. Duplicate samples were collected during Occoquan-II, one of
which was dechlorinated immediately to stop the haloform
reaction; the other was allowed to stand a minimum of seven
days at room temperature prior to analysis. During Occoquan-I,
only one sample was collected and it was not dechlorinated. Too,
all samples were kept at 0-5°C until they were analyzed.
3. Precise procedures for sample handling and storage prior to
analysis were specified during Occoquan-II to ensure that all
37
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samples were treated uniformly. During Occoquan-I, samples
were stored in ice immediately after collection and during
shipment and then in a refrigerator at 0°-5°C before analysis.
4. During Occoquan-II, sampling from the Bull Run sites was dis-
continued and a third site in the distribution system was added.
These differences, coupled with the fact that the climatological conditions
were quite different during the two years, have made it desirable to present
and discuss the data collected during phases I and II separately before they
are considered together.
It should be mentioned that since this project began in 1975, much
research data has been published on a variety of topics related to the
reduction and control of volatile organics, particularly the trihalomethanes
(THM), in public water supplies. On February 9, 1978, the EPA published
proposed amendments (8) to their previously published Interim Primary
Drinking Water Regulations (2) that dealt specifically with the control of
organic contaminants in drinking water. A MCL of 100 yg/1 total THM (TTHM)
was proposed, that value being the average of the concentrations of the THM's
detected in samples of finished water which are dechlorinated at the time of
collection. In this section of the report, part of the data analysis will be
discussed in relation to that proposed MCL and, in addition, some discussion
will be given to a consideration of factors the authors believe influenced
the THM concentrations in FCWA's finished water. Of course, it was recog-
nized, even as this report was being written, that research is continuing
and new data may either substantiate or refute some of the interpretations
of the data presented herein.
Occoquan-I; 1975-1976
Frequency and Distribution—
Table 16 shows the frequencies that volatile organics were detected in
samples of raw and finished waters during the first year of the program.
Both CHC13 and CHBrCl2 were present in all finished-water samples; and CHC13,
though present in lower concentrations, was detected in the majority of the
raw water samples. Table 17 compares the concentrations of CHC13 (the THM
always present in highest concentrations) in raw and finished water. These
data demonstrate what both Rook (9) and Bellar et^ al. (10) showed earlier,
namely that chlorination of natural waters is responsible for THM formation.
Note from Table 17 that the addition of several million gallons of treated,
chlorinated sewage to Bull Run (dilution approximately tenfold) did not
appreciably increase the CHC13 concentrations above those measured in samples
from a station above the treatment works. Chloramines, the only chlorine
forms in effluents containing ammonia, are generally the only chlorine species
present in sewage effluents, and they do not react with organic precursors to
form THM's (11).
Figure 4 shows that the THM concentrations observed in finished water
during the entire Occoquan Study (phases I and II) were most likely normally
distributed. (The data-fit on log-normal probability paper did not approxi-
mate a straight line). The distribution pattern is an important consideration
39
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in determining whether certain data-analysis procedures are valid. Symons
e_t al. (12) reported previously that the data collected during the National
Organics Reconnaissance Survey (NORS) involving eighty water supplies from
several types of sources were log-normally distributed.
The individual data for finished water samples during June through
September from which Table 18 was constructed are shown graphically in
Figure 5. In general, the THM concentration in weekly grab samples seemed
to increase and decrease similarly at Sites D, E, and F during June and
July, 1975. During this period, there did not appear to be a consistent
order of THM concentrations (e.g. E>F>D). Often, the concentrations at the
treatment plant were greater than at one or more of the distribution system
sites. In late July and during August, however, the lowest concentrations
were observed at the treatment plant, as one would expect. It should be
remembered that during the first year, the samples were refrigerated until
the time of analysis and were not dechlorinated, so care must be taken in
generalizing about trends in the data because there is no way of knowing
whether the total THM formation potential (THM FP) had been reached. What
is clear from Figure 5 is the concentration of THM's steadily increased
during June and July and began to decrease in late August. The resurgence
during early September occurred immediately after a two-day period of heavy
rainfall on September 11 and 12.
Figure 6 shows the observed hourly variations in THM's at Sites D, E,
and F. One observation evident from this figure is that the variations
were more pronounced at Site F during the twenty-four hour period, indicating
that the intermediate storage and rechlorination at Cameron Station may have
a definite effect. The bihourly variability also suggests that the time of
day when sampling occurs will affect the observed THM concentration, but
there most likely is no well defined diurnal pattern. It was noted that
the average bihourly concentrations on September 11 were significantly greater
than the average daily concentrations observed the week of September 10
through 16. Figure 5 shows that concentrations were greatly decreasing during
that particular week, but the data certainly suggest that "average concentra-
tions" one might cite for a given system may have an associated high varia-
bility which is dependent upon the time of sampling. Another source of
variability which should be considered is in the THM analysis itself. The
precision of the Bellar-Lichtenberg THM analysis has been shown to be on
the order of ±10 percent (13). More discussion about variations in THM con-
centrations with time of sampling will be presented in a subsequent section.
Table 18 and Figures 7 and 8 show that the highest THM concentrations
were observed during the summer months during the first year of the study.
Chloroform accounted for about 90 percent of the TTHM concentrations observed
on all occasions, CHC^Br accounting for most of the remainder. Both CHBr3
and CHBr2Cl were seldom detected. Figures 7 and 8 show, respectively, the
observed variations in TTHM's and CHCl2Br at the treatment plant during
Occoquan-I. A definite trend was evident, the highest concentrations
occurred during the summer months and the lowest during the winter. Patterns
of TTHM variations at the other finished-water sampling sites were similar to
those depicted by Figures 7 and 8. During Occoquan-II, the patterns were
different, a fact that will be discussed later.
43
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Comparison With Other Studies—
Table 19 was prepared to show how the Occoquan-I THM data compared to
that obtained during two other EPA-sponsored surveys. The NOMS data dis-
played in Table 19, was taken from the Federal Register C8), and are those
derived from the first of four phases. Similar collection and handling
procedures were used during NORS and NOMS-I and best represented those used
during Occoquan-I. The TTHM concentrations in Table 19 are summations of the
observed concentrations of all THM1 s in micrograms per liter instead of in
micromoles per liter. This method of expressing the data weights the bromi-
nated THM's more heavily than the less toxic chloroform and, in addition, is
a simpler method for expressing the data than that required to express it in
terms of micromoles per liter.
It should be noted that both the NORS and NOMS studies represent a
variety of water sources. For example, the NORS study included localities
that took their raw water from ground water sources (20 percent), lakes or
reservoirs (33 percent), and rivers (47 percent). Too, the data in both the
NOMS and NORS studies were conducted in the winter months. From Table 19,
it can be seen that while the average TTHM was much higher in the Occoquan
study, the maximum values observed in each study were comparable.
The individual data used to compute the values found in the figures and
tables presented thus far in this section of the report appear in Appendix C,
Tables C-l through C-ll. Some data appearing there have not been discussed
thus far in any detail, and a few should be mentioned because they are
unusual. For example, Tables C-5 and C-6 show that during the bihourly
sampling on September 11, CHCl2Br appeared only at Site F in Alexandria,
Virginia. Chlorine is applied when water is taken from the open storage
reservoir during peak demand periods to supplement the supply coming directly
from the FCWA plants, but the chlorine supplier is the same for both FCWA and
the Virginia-American Water Company in Alexandria. Thus far, no explanation
has been found for the more frequent appearance of CHClBr2 at Site F (Tables
C-6 and C-7). Finally, note from Table C-7 that 1,2-DCE + CCl^ appeared most
frequently in Bull Run (Sites A and B) and, with one exception, in higher
concentrations than were observed elsewhere. Separation of these two volatile
organics was not attained until late in the Occoquan-I study when the analyti-
cal procedures were modified. No explanations are apparent for the presence
of 1,2-DCE and CC14 in Bull Run during Occoquan-I, nor for the high concentra-
tion (34 yg/1) noted on June 9, 1975, in finished water at the treatment
plant (Site D). Neither CC14 or 1,2-DCE were observed at Sites E and F.
Occoquan-II: 1976-1977
Frequency and Distribution—
Table 20 shows the frequency the haloforms and other volatile organics
appeared in finished water at four finished-water sites. (See Appendix C,
Tables C-12 through C-16 for the individual data.) As was true during
Occoquan-I, CHClo and CHC^Br were present in every sample. The concentra-
tions of CHBr2Cl were always less than 5 yg/1 (usually less than 2), though
it was detected from 45-55 percent of the time. Carbon tetrachloride (CCl^)
and 1,2-dichloroethane (DCE) appeared more frequently in finished water than
49
-------
TABLE 19. COMPARISONS OF HALOFORM CONCENTRATIONS OBSERVED DURING
THE NORS, NOMS, AND OCCOQUAN-I STUDIES
Concentrations Observed,
Halof orm
bNORS
Jan-Feb, 1975
bNOMS-I
Mar-April, 1976
yg/1
COCCOQUAN-I
June, 1975
May, 1976
Chloroform
mean
median
range
Bromodichlorome thane
mean
median
range
dTotal Trihalomethanes
mean
median
range
21
nf-311
.
6
nf-116
67
27
nf-482
43
27
nf-271
18
10
nf-183
68
45
nf-457
246
243
22-495
19
18
-------
TABLE 20. FREQUENCY OF VOLATILE ORGANICS GREATER THAN
OR EQUAL TO ONE MICROGRAM PER LITER AT ALL
SAMPLING SITES. JUNE. 1976-MAY. 1977
CHC1 CHBrCl CHBrl CHBr CC1 1,2-DCE
Obser- 3 2
Site vations No. % No. % No^% Ncxi% NoTX NcT.%
C21 3141 500000000
D 21 21 100 21 100 10 48 2 10 4 19 1 5
E 20 20 100 20 100 11 55 0 0 5 25 1 5
F 20 20 100 20 100 9 45 0 0 2 10 1 5
G 20 20 100 20 100 9 45 5 25 2 10 1 5
Site C: Intake, FCWA water treatment facility.
Site D: Finished water, FCWA water treatment facility.
Site E: Distribution system, FCWA's storage yard.
Site F: Distribution system, Alexandria, Virginia.
Site G: Distribution system, Dumfries, Virginia.
*Includes 10 monthly samples and 5 daily samples for each of the
other two months. Two samples were collected in June at Sites C and D.
51
-------
during Occoquan-I, and concentrations as high as 7 and 9 yg/1, respectively,
were observed. Recall that it was not until February 8 that DCE and CCl^
were separated during the analysis, and thereafter low concentrations of
CC14 began to be detected, especially during March through May, 1977. DCE
appeared only in the February samples, and it was detected in all of the
finished-water samples. Bromoform (CHBr-j) was detected only at Site D at 3
and 1 yg/1 on March 7 and 8, respectively.
which is not a product of reactions between organics and chlorine,
has been identified in the District of Columbia's drinking water at 5 yg/1
(14). The EPA 80-City Study (NORS) showed that CC14 was present at 10 loca-
tions in concentrations of 3 yg/1 or less, and 1,2-DCE (ethylene dichloride)
was present in 26 supplies in concentrations ranging from 0.2-6 ug/1 (12).
It also has been found in the New Orleans water supply at a concentration of
8 yg/1 (17). The EPA lists both these compounds as industrial contaminants,
and CC14 has been found in deionized water dosed with commercial chlorine gas
in concentrations ranging from about 1 to 40 yg/1 (Personal communication,
Mr. William M. Blankenship , Technical Advisor , USEPA Region III, Philadelphia).
Table 20 also shows that CHCl^ was detected in raw water only on three
occasions (14 percent of the time) during Occoquan-II. This contrasts with
the high frequency of detection at Site C during Occoquan-I (62 percent) .
Note also that CHBrC^ was the only other volatile organic detected in raw
water during Occoquan-II, and that was only on one occasion. Table 21
summarized the significant data concerning THM concentrations observed at
each finished-water sampling site during Occoquan-II. It can be seen that
the average concentrations at Sites D, E, and F were nearly the same, but at
Site G, which is the most distant in the distribution system, the concentra-
tions averaged about 15 percent greater. Also, the average, free-chlorine
residuals were lowest there (Table 22) , this being especially true during the
summer months. The individual data used to calculate the statistics shown
in Table 21 are in Appendix C, Tables C-12 through C-16. Those used to
calculate the statistics regarding chlorine concentrations are found in
Appendix D, Table D-2.
THM Concentrations in Dechlorinated Samples —
During Occoquan-II, duplicate samples were collected on each sampling
date and one of them was dechlorinated immediately so that the instantaneous
THM concentration could be measured. (This procedure was followed also during
NOMS-III to be discussed briefly in a subsequent paragraph) . The results of
these analyses are summarized in Figure 9 which shows the mean THM concentra-
tions and standard deviations associated with those means at the four
finished-water sites sampled during Occoquan-II. The significance of this
particular THM measurement at any location is that the instantaneous con-
centration more closely approximates the THM level of exposure to the con-
sumer than does the "terminal" THM concentration, i.e., that which is obtained
when reactions are allowed to go to completion, at least under the constraints
of the available chlorine and reactable organic matter present at the time of
sampling .
In Figure 9, the bars representing the sampling stations were arranged
from left to right in increasing order of the hydraulic travel time from
52
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53
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TABLE 22. COMPARISONS BETWEEN TRIHALOMETHANE AND CHLORINE
CONCENTRATIONS OBSERVED AT FCWA'S TREATMENT PLANT
AND AT THREE SITES IN THE DISTRIBUTION SYSTEM:
MAY, 1976 - JUNE, 1977
Site
Statistic
TTHM, pmol/1
Terminal
Chlorine Residual, aig/l
Dechlorinated Total Free
mean
median
range
stnd. dev.
1.35
1.12
0.59-2.16
0.55
0.84
0.79
0.32-1.47
0.36
2.7
2.5
2.1-4.2
0.6
2.5
2.5
1.9-3.5
0.5
mean
median
range
stnd. dev.
1.37
1.26
0.64-2.34
0.53
0.93
0.82
0.35-1.71
0.45
2.5
2.5
1.2-2.9
0.3
2.2
2.2
1.1-3.2
0.3
mean
median
range
stnd. dev.
1.35
1.33
0.6 -2.22
0.50
0.94
0.86
0.35-1.63
0.40
1.9
1.9
0.8-2.4
0.6
1.6
1.6
0.7-2.5
0.5
mean
median
range
stnd. dev.
1.56
1.36
0.84-2.70
0.55
1.42
1.35
0.38-2.72
0.59
1.1
1.0
0.2-2.7
0.7
0.9
0.8
0.1-2.3
0.6
54
-------
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- — ANNUAL MEAN
STANDARD DEVIATION
h ( ) PEAK OBSERVED
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i
(330)
m
m
PEG
SAMPLING SITE
Figure 9. Instantaneous TTHM concentrations in dechlorinated finished
water at four sites during Oecoquan-II. (One standard
deviation on either side of the mean is shown for each site.)
55
-------
the treatment plant (Site D). These were, for Sites F, E, and G, 8, 10, and
13 hours, respectively. (The intermittent reservoir in Alexandria was ignored
in the calculation of travel time for Site F since it contributed flow only
after 4:00 p.m., a later time than when all samples were collected there).
It seems clear from the data that the only significant difference, as was
the case for the samples which were not dechlorinated (Table 21), was at
Site G where the mean THM concentrations averaged about 35 percent greater
than at Sites D, E, and F. Table 21 summarizes the statistical information
shown graphically in Figure 9.
Comparison With Other Studies—
Tables 23 and 24 summarize the measured concentrations of CHC13,
CHCl2Br, and TTHM (as yg/1) observed at all finished-water sampling sites
during Occoquan-II and compare the statistical data to those obtained during
various phases of the NOMS study (8) of 113 cities. Samples collected during
NOMS-II, NOMS-III, and Occoquan-II were treated similarly in that samples
stood for a sufficient time at room temperature before analysis to ensure
that the reactions could go as far toward completion as the concentrations
of the reactants would permit. Some, of course, may have been limited by
the availability of chlorine. In both NOMS-III and Occoquan-II, a second
sample was collected on every sampling date and dechlorinated immediately.
On the average, the instantaneous THM concentration was 72 percent of the
"terminal" concentration during Occoquan-II but only 45 percent in NOMS-III.
However, NOMS-III was conducted during the period from November, 1976 through
January, 1977, when the water temperature was low, a condition which would
cause the haloform reaction to proceed more slowly than during warmer weather.
In January during the Occoquan-II study, the concentrations of THM's in the
three of the four dechlorinated samples were only 45-48 percent of the
terminal concentration. Figure 10 shows the observed relationship between
the temperature and CHC13 in dechlorinated samples expressed as a
percentage of the terminal concentration. There is considerable scatter in
the data which was caused by a variety of factors (reactant considerations,
time of travel to sampling site, time elapsed since chlorine added, etc.)
but the general trend is obvious: the colder the water, the smaller the
percentage of the terminal CHC13 concentration at the tap. There was no
well-defined relationship between the individual instantaneous THM concentra-
tions and temperature, however.(See Figure 11.)
Note from Table 23 that the high TTHM value was nearly 900 ug/1- This
value was observed on August 9 at Site D on the first of the five consecutive-
day sampling programs. A second sample collected within minutes of the first
showed a concentration of 869 ug/1 CHC13. A search of the water treatment
plant records failed to turn up an irregularities in the normal plant opera-
tions, and the other water quality data routinely collected at the plant were
not unusual in any respect. The cause of this event is unknown, and it is
difficult to speculate how concentrations of organic carbon might be so high
at that one period. The phenomenon was never again observed.
It should be noted that Occoquan-II sampling represented an entire year
whereas NOMS-II and III were conducted during three-month periods in two
different seasons, and the data may well reflect seasonal variations. One
thing is clear, though: as was true for THM concentrations observed during
56
-------
TABLE 23. COMPARISONS OF HALOFORM CONCENTRATIONS OBSERVED
DURING THE NOMS AND OCCOQUAN-II STUDIES.
aTerminal Concentrations Observed, U8/1
bNOMS-II bNOMS-III COCCOQUAN-II
Haloform May-July, 1976 Nov. 1976- June 1976-
Jan. 1977 May 1977
Chloroform
mean
median
range
Bromodichlorome thane
mean
median
range
Total Trihalomethanes
mean
median
range
83
59
nf-470
14
18
nf-180
117
87
nf-784
69
44
nf-540
11
17
nf-125
100
74
nf-695
152
d 136
40-858
21
22
3-50
173
164
43-889
"Terminal": reactions allowed to go to completion, nf-not found
Reference 8
Monthly values were used for calculations of means and medians. The Aug.
1976 and Mar. 1977 values were averages of analyses on five consecutive
days (four finished-water sampling sites). These daily values were con-
sidered when stating the ranges, however.
The high value was nearly three times that of the next highest.
Without it, mean - 116, median » 115, high - 329.
57
-------
TABLE 24. COMPARISONS OF HALOFORM CONCENTRATIONS IN
DECHLORINATED FINISHED WATER SAMPLES COLLECTED
DURING THE NOMS AND OCCOQUAN-II STUDIES
Halofonn
Observed Concentrations, ug/1,
in Dechlorinated Samples
NOMS-IH
•QCCOQUAN-II
Chloroform
mean
median
range
Bromodichloromethane
mean
median
range
Total Trihalomethanes
mean
median
range
35
22
nf-200
9
6
nf-72
53
37
nf-295
109
97
19-310
15
16
3-28
125
115
25-330
nf=not found
Reference 8
Ilonthly values were used for calculations of means and medians. The Aug.
1976 and Mar. 1977 values were averages of analyses on five consecutive
days (four finished-water sampling sites). These daily values were con-
sidered when stating the ranges, however.
58
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60
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Occoquan-I, the FCWA's finished water consistently contained higher mean
concentrations of THM's than was found in the NOMS studies. Finally, Tables
23 and 24 compare the concentrations of only the two most abundant THM's.
Appendix Tables C-12 through C-16 provide the data which could be used to
calculate similar statistical information for other volatile organics. These
values were not included in Tables 23 and 24 because of their infrequent
occurrence in FCWA's finished water.
Total Organic Carbon (TOG)—
A requirement of the contract regarding Occoquan-II was that TOC concen-
trations in the samples were to be determined. The individual TOC data are
displayed in Appendix C, Tables C-12 through C-16. Raw water TOC concentra-
tions averaged 4.2 mg/1 (range 2.4 - 11.5). Until April, 1977, all TOC
analyses were conducted with the Beckman 915A instrument (20 mg/1 full-scale
deflection). In April and May, the Dohrmann/Envirotech Model 54 analyzer,
which permitted analyses with parts per billion accuracy, was used. For all
data pertaining to finished-water TOC concentrations, the mean was 2.4 mg/1
(range 1.0 - 7.0). During the last two months when the more sensitive
instrument was used, the average was 1.4 mg/1 (range 1.1-1.6). An attempt
was made to correlate the finished-water TOC concentrations with the THM
concentrations, and the correlation was extremely poor.
Young and Singer (15) noted similar results during a study of THM's
produced during treatment of water from two separate reservoirs in North
Carolina. They noted that "... there is little seasonal variation in
[nonvolatile] TOC (NVTOC) levels in raw water. However, fluctuations" in the
amount of CHC13 produced during water treatment suggest fchat it is difficult
to predict the finished water concentration on a given day solely on the
NVTOC concentration." Their reasoning that "NVTOC is a collective measure
of all organic constituents, only a few of which are CHC13 precursors"
provides the explanation for the lack of linear correlation between THM's
and TOC in the Occoquan Project.
In the Occoquan Reservoir, or in any other for that matter, the organic
matter entering several miles above the dam tends to be well stabilized by
bacterial degradation by the time it reaches the raw water intake. While
there no doubt are biologically mediated organic compounds available that
will react to form haloforms, most of the TOC merely exerts a chlorine
demand or forms chlorosubstituted organics other than trihalomethanes. One
can speculate that the TOC entering rivers by way of runoff is likely to
be less stabilized and, hence, more reactive in producing THM's. Wood and
DeMarco (16) have reported that TOC data did not consistently correlate with
the THM formation potential of well water from humate-laden aquifers in
Florida (av. TOC, 9-10 mg/1). They also reported that only about 35 percent
of the TOC could be removed by coagulation, flocculation, clarification,
and filtration combined. At FCWA, TOC removals varied considerably during
treatment, but averages were from 50 to 70 percent. Still, concentrations
of TOC greater than 1.0 mg/1 were consistently found in the finished water.
Comparison of Occoquan-I and Occoquan-II THM's
61
-------
Table 25 presents a comparison of the average TTHM concentrations (and
other statistics) observed during Occoquan-I and Occoquan-II. The data are
grouped by intervals of three months to demonstrate, to some degree, the
seasonal variations that occurred. It is obvious that there were seasonal
variations during both years, but the patterns of fluctuation differed. In
1975-1976, the highest concentrations occurred during the summer, but during
1976-1977, the highest concentrations were not observed until the fall.
Furthermore, the average high concentrations observed during Occoquan-I were
approximately a third greater than those observed during Occoquan-II.
In Figure 12, the average THM concentrations observed at each finished-
water site during the two-year study are depicted along with the annual mean
for all sites. The means at each site were calculated by averaging monthly
values. If analyses were performed weekly, then the monthly average was
calculated from four or five values. When the frequency was daily, an
average was obtained and considered to be a weekly value. Bihourly samples
were averaged to give a single daily value. From Figure 12 one can see that
the annual average THM concentration was slightly lower the second year of
the study. During both Occoquan-I and Occoquan-II, concentrations of THM's
in non-dechlorinated samples from the distribution system were both less than
and greater than those in samples from the treatment plant. There was no
definite pattern.
Several facts must be kept in mind if Figure 12 is to be properly inter-
preted. First, the estimated hydraulic travel time to Site E from the New
Lorton Plant is two hours greater than to Site F, but there is intermediate
storage at Site F and the water is rechlorinated at the time it reenters the
distribution system. Second, Site G, though furthest from the treatment
plant, receives water only from the Occoquan Plant (See Table 2). The other
two sites receive a mixture of water from all three of FCWA's treatment
facilities. If there is to be a direct comparison of THM's found at Sites
D, E, and F with those at G then an assumption must be made that the THM
concentrations in Occoquan Plant water were similar to those in the mixture.
The assumption is probably valid since all three plants have a common raw-
water intake. Third, data previously presented in this report and summarized
in Table 25, clearly show that the THM concentrations were highly variable
from season to season. Even the bihourly analyses showed that there was con-
siderable variation in THM concentrations in water from the same site.
Therefore, the slight differences in average THM concentrations shown by
Figure 12 are not statistically different because the standard deviations
are so high. It appears that the THM concentrations in non-dechlorinated
samples could have been taken as representative of those in the distribution
system.
It is true that the sampling frequency was greater for part of
Occoquan-I (during June-October), but the differences observed during the
two phases of the study are more likely related to differences in water
quality in the two years of the study. The second year was extremely dry,
and the water quality at the dam site improved. The rainy season did not
begin until October, 1976, and it was in October and November that the
highest TTHM values were observed.
62
-------
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Data Selection for Determining an Average THM concentration
The proposed interim regulations for organic compounds (8) describe
methods to be followed in determining the average THM concentration for a
given system. A minimum of five samples is to be taken quarterly: no more
than 20 percent from the treatment plant and the rest from the distribution
system, 20 percent of which must be from extreme points in the system. The
quarterly averages of these samples provide the basis for calculating the
yearly average.
Figure 13 shows the results of an analysis carried out with the
Occoquan-II data base. The monthly samples (or average of five days in
March and August when analyses were on a daily basis) were grouped in three
combinations for calculating the quarterly averages. First, the THM concen-
trations for January, April, July, and October at each of the sites (D, E,
F, and G) were averaged. Then, those for February, May, August, and November
were averaged; and finally, those for March, June, September, and December
were averaged. As can be seen in Figure 13, the yearly averages that would
be obtained by computations with the three groups of "quarterly data" differ
by as much as 40 yg/1, and two of the three group averages deviate signifi-
cantly from the annual mean of pooled data from all sites. This analysis
considered the THM's only in undechlorinated samples, which probably closely
represents the "terminal" TTHM value that could have developed. A similar
analysis was conducted with the data for TTHM concentrations in dechlorinated
samples. The three "annual means" were 127, 142, and 105 pg/1 for the three
arrangements of monthly samplings shown in Figure 13 (corresponding to Annual
Mean -I, -II, and -III, respectively). The annual mean for all data pooled
was 125 yg/l~. It is evident that these quarterly averages differed as much
as those used in the previous calculations.
These results point out a potential bias that both the utilities and
regulatory personnel should be aware of. There is no specific recommenda-
tion that can be made based on data derived during this study, though perhaps
some scheme might be devised for compositing several samples over at least
a 24-hour collection period. However, even that approach, if it were tech-
nically feasible and practical, would not be sufficient to compensate for
the extreme variability that was observed.
Relationships Between Finished-Water THM's and Raw Water Quality
An Analysis of all available pertinent water-quality data collected
routinely by FCWA and the Occoquan Watershed Monitoring Program was undertaken
to determine if some correlations could be made between raw-water quality and
finished-water THM concentrations. This study was undertaken because the
variations in THM concentrations appeared to be of a seasonal nature, both
during Occoquan-I and Occoquan-II. The need for such a study became even
more apparent when it became evident that the seasonal variations during the
two years of the entire study did not follow the same trend, a fact discussed
in the preceding section.
Theoretical Considerations—
65
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Some clue as to which water-quality parameters may be important is given
by an examination of the equation for the haloform reaction: In word form,
the reaction can be stated as follows:
halogen + precursor organics •> haloform + other organics
In more precise chemical form, the equations that illustrate the overall
reaction, using chlorine as the halogen (in its hypohalous acid form) are:
CH3COR + 3HOC1 •* CC13COR + 3H20 [1]
CC13COR + H20 •> RCOOH + CHC13 [2]
The organics in equation [1] are the precursors and are thought to be com-
pounds containing acetyl groups or others, like secondary alcohols, that
can be oxidized to form acetyl groups. Rook (9) first demonstrated that
the naturally occurring humates could serve as precursor organics. Recently,
Thompson (16) and Barnes (19) showed that laboratory cultures of algae produce
an abundance of THM precursors, especially during their active-growth stages.
Chlorine, of course, is the other necessary reactant, and it is present in
abundance during routine water treatment.
Other factors are known to affect the haloform reaction, especially the
rate. Obviously, temperature would affect the rate according to Arrhenius'
rule, but pH affects not only the rate but also the absolute yield of halo-
forms. Reaction [2], the hydrolysis step, is highly dependent on pH. [Morris
(20) has presented excellent discussion of the haloform-reaction chemistry for
those who wish tothave a more thorough understanding.]
It seems, then, that during normal water treatment operations, provided
there is adequate time for all reactions to go to completion, the maximum
THM concentration one might expect in finished water would be a function of
at least four variables: 1) the concentration of precursor organics in raw
water, 2) the chemical nature of the precursors (i.e., whether the appro-
priate functional groups are present), 3) the quantity of chlorine applied
during water treatment, and 4) the pH of the water during or after treatment
when chlorine is present. Some factors that should reflect the availability
of THM precursors in raw water have been listed in Table 26 along with a
discussion of the ways they might contribute.
Analytical Approach—
All the available data were accumulated and analyzed by a series of
statistical procedures to determine if some multiple-regression expression
could be developed to relate finished-water TTHM concentrations to direct
or indirect measures of water quality. The procedures chosen were on avail-
able computer programs at VPI & SU as parts of a statistical analysis
system (SAS). The programs included a "backward elimination routine," a
"stepwise elimination routine," and a determination of maximum R2 values
(R = correlation coefficient in a regression analysis). Once the best-fit
to the data was obtained, an analysis known as the "Press," was applied to
the multiple-regression equation to determine if the equation was truly
67
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TABLE 26. PHYSICAL, CHEMICAL, AND HYDROLOGICAL FACTORS
THAT MAY ALTER RAW WATER QUALITY AND SUBSEQUENT
TRIHALOMETHANE CONCENTRATIONS IN
FINISHED DRINKING WATER
Indicator
Possible Significance
Reservoir Turbidity & Color,
Rainfall & Reservoir Stage,
Raw-Water Chlorine demand
Increases would indicate influx of
land runoff or reservoir destratifi-
cation, both of which should increase
THM-precursor availability.
Reservoir Surface pH and Dis-
solved Oxygen Concentrations
(during daylight hours);
Chlorophyll-a Concentrations
Increased algal activity would in-
crease both pH and dissolved oxygen
and provide THM precursors through
the excretion of extracellular products
and by providing cell mass.
Reservoir-Bottom Dissolved
Oxygen Concentrations
When less than 0.5 mg/1, or about 5%
saturation, anaerobic decomposition
of organic matter in sediments and
water would produce THM precursors.
Raw-Water Total Organic Carbon
& Carbon Chloroform Extracts
Both are indirect indicators of the
presence of potential THM precursors.
68
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predictive and, hence, a "model" of the system. It is beyond the scope of
this report to provide details of the statistical package used in the com-
puter analysis, but the significant results are discussed in the following
paragraphs.
Correlations between TTHM's and other available data— Each of the water-
quality parameters and other data that might be useful in predicting the TTHM
concentration in finished water were tested for correlation by a simple,
linear least-squares regression analysis. Both Occoquan-I and Occoquan-II
data were used in the analysis, but only the average TTHM concentrations at
Sites E and F, which were common to both years of the study, were considered.
Concentrations at Site D were, at times, lower than at Sites E and F (espec-
ially in winter) because there was not always sufficient time for the haloform
reaction to approach completion. Site 6 was not included because it was not
sampled during Occoquan-I. Table 27 summarized the linear regression co-
efficients found to be associated with the various analyses. One precaution
which should be interjected at this point is that a low correlation coeffi-
cient obtained by a simple linear regression analysis does not preclude the
appearance of the associated variable in a multivariant equation.
It is obvious that raw water total organic carbon (TOG) and carbon
chloroform extract (CCE) concentrations were not highly correlated with the
terminal TTHM concentrations. It is likely that the nature of the organic
compounds change with time during the year and not all the TOG (or CCE) will
enter the haloform reaction. The high correlations with temperature and
chlorine demand and dose were not surprising in light of the observed seasonal
variations in- TTHM concentrations previously discussed. Temperature data
were not included in the multiple regression analysis, however, because the
THM concentrations considered were the terminal concentrations, or at least,
those in samples that had not been dechlorinated. Also, the high positive
correlation more likely reflects the improved quality of the reservoir in
the winter.
The pattern of TTHM variations in relation to those for chlorine (applied
and residual) are shown in Figure 14. The chlorine demand was calculated by
subtracting the total residuals observed at the tap from the dose applied,
both during pre- and post-chlbrination, at the treatment plant. The general
pattern is obvious: the chlorine demand fluctuated in approximately the same
manner as did the TTHM concentrations. The dose applied, as shown in Figure
14, is the weighted averaged dose at all three of the FCWA treatment plants
(discussed in Section 1). The chlorine demand of Occoquan Reservoir water
increases during the summer because reduced iron and manganese are both
present in high concentration, but, apparently, the available organic com-
pounds, which also exert a chlorine demand, are high THM-yielding precursors.
The relationship apparently is a complicated one and is not adequately
described by a simple relationship between TOG and chlorine demand or THM
concentration. Even color and turbidity did not correlate well. Young and
Singer (14) also reported poor correlations between color and THM's.
It certainly would be convenient for the treatment plant personnel to
be able to substitute some easily measured water quality charactersitic for
the THM analysis. However, no reliable surrogate could be found among the
69
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TABLE 27. RESULTS OF LINEAR LEAST SQUARES REGRESSION ANALYSES
BETWEEN FINISHED-WATER TRIHALOMETHANE CONCENTRATIONS AND
RAW WATER QUALITY
Parameter
Secchi disk, in.
Color units
Reservoir stage, ft.
Turbidity, JTU's
Correlation
Coefficient
0.14
0.20
0.24
0.25
Number of
Observations
21
36
36
37
TOG, mg/1
Surface 0.25 21
Bottom 0.46 20
CCE, yg/1 0.28 11
Dissolved oxygen, % saturation
Surface
Bottom
Rainfall, in. /mo.
pH, surface
Temperature, surface, °C
fchlorine demand, mg/1
Chlorine applied, mg/1
0.35
0.75
0.54
0.57
0.75
0.75
0.75
19
19
37
24
22
37
37
Calculated by subtracting the chlorine residual from the chlorine dose
applied at the treatment plant
70
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o.o
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2.5
_ 2.0
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-
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i 1.0
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11 ill i i i i i | i i | i i I I i I I
r r~^ AV. TTHM CONG., ALL FINISHED- WATER
/ \ >SITES (non - dechlorinated samples)
\ A *
! •' * A
/ \ / \
\
• \ i ^
* \ m
' ^ ' *>• ^A
V ,'^ / X / \
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— \ ' v* \ / —
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II III III II III 1 1 1 1
II III III II ill till
/°X .TOTAL APPLIED DOSE AT TREATMENT
/ \ if PLANT
v ^^^ ^^\^
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AV. TOTAL RESIDUAL, FINISHED-WATER
^ SITES^^^
/ S^0^'*S^a_ ^. ^^ <^~— •«-
~*^-^'*~~* ~^+'' ~^^^^^^-^^' ^-o~
II III 1 1 1 1 1 1 111 11
JUN|JUL|AUGSEPJOCT]NO\|DEC JANFEBJMARJAPRJMAY|JU^JULJAUQ SEP|OCT|NOVJDEC JANFEBMARJAPRJMAY
1975 1976 1977
Figure 14. Variations in TTHM concentrations, chlorine dose, and
chlorine residuals in finished waters, June, 1975 -
May, 1976.
71
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available Occoquan Reservoir data except, perhaps the chlorine demand test.
Even that relationship was only moderately well described by a linear rela-
tionship. Perhaps it is fallacious to expect that the myriad of complex
variables affecting both water quality and the trihalomethane-forming chemi-
cal reactions could ever be adequately described by a simple linear rela-
tionship. That possibility is attractive, nevertheless, and perhaps one
eventually can be found that is applicable, if not universally, at least to one
particular treatment plant.
Results of the Multiple Regression Analysis—
The multiple regression analysis identified two water-quality character-
istics (dissolved oxygen concentration and chlorine requirement) and two
hydrology-related characteristics (rainfall and reservoir stage) that were
highly correlated in formulating an empirical relationship with the observed
finished-water TTHM concentrations. A description of the statistical proce-
dures and the "best-fit" equations which resulted from the analysis are
found in Appendix E. The terms included in these equations are indicators
of: 1) algae growth(dissolved oxygen at the reservoir surface, which often
was supersaturated), 2) the influx of THM precursors from the surrounding
watershed (rainfall and stage), 3) the overall water quality in the reservoir
(chlorine applied and chlorine demand).
The equations which were developed, while serving to describe the data,
did not prove to be true models of the system because they were not predic-
tive (See Appendix E for the explanation). More data than axe available are
needed to calibrate and verify any model, and it may be that it will be
impossible to account for all the conditions that influence THM production
in a surface-water source like the Occoquan Reservoir.
Relationships to Algae Growth—
Hoehn et al. (21) reported that a good relationship was observed between
chlorophyll-a concentrations in the raw water and the TTHM concentrations in
FCWA finished water (See Figure 15). Chlorophyll concentrations indicate the
density of algae populations within the reservoir but are not as precise as
other measures,such as cell numbers, areal standards units of algae, etc.
Chlorophyll data were not included in the statistical analysis just completed,
but other statistical procedures, which will include the algae-related data,
are being evaluated to determine if a model can be developed.
As has been previously mentioned, the finished-water TTHM concentrations
during the summer of 1976 were considerably lower than during the summer of
1975. It was also observed that the average raw-water chlorophyll-a concen-
trations also were lower during the summer of 1976 (12 ug/1) than during a
similar period in 1975 (44 pg/1). During the summer of 1976, there was
considerably less rainfall, which markedly decreased the runoff contributions
of fertilizer nutrients (phosphorus and nitrogen) that encourage algae growth.
The decreased runoff also reduced the humate contributions from the surrounding
watershed as well, but the relationship between algae and TTHM, as shown by
Figure 15, indicates that algae as contributors of THM precursors cannot be
ignored. The summer of 1977 was not included in this project period, but the
72
-------
•t.o
| 4.0
=4,
0
<•> 3.0
UJ
< 2.5
X
H
g 2.0
o
< 1.5
x
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Figure 15. Relationship between concentration of chlorophyll-a
concentrations in the Occoquan Reservoir and finished-
water TTHM concentrations during the summers of 1975
and 1976. (Only single values were available for June,
July, and August, 1976. There was no September
measurement).
73
-------
Occoquan Monitoring Program continued, and the data showed that the algal
growth-limited by the absence of adequate phosphorus at the dam. That year
was a severe drought year, and the reservoir stage reached its lowest point
since the high dam was constructed more than a decade ago. Some data
collected independently by the authors.during the summer of 1977 showed that
the finished-water TTHM concentrations at Site D were less than the pro-
posed MCL of 100 pg/1, which is further evidence that conditions which favor
high THM concentrations, namely high humate concentrations and increased
algae growth in the raw water, are related to rainfall and, hence, runoff.
Special Studies
In addition to the routine THM monitoring program, two special studies
were conducted— one to determine if any changes in finished-water THM con-
centration would occur with time of water flow from the tap and the other to
determine if significantly greater concentrations of THM's were present in
filter back-wash water at the treatment plant than in the finished water
passing through the filter. These studies are discussed in the following
paragraphs.
THM Concentration Variations with Time of Flow From Tap—
On two occasions (June 8 and 15, 1977) samples at Site G were collected
for analysis at small time intervals after the tap was opened. The objective
was to determine if the THM concentrations observed at a given location might
be affected by the length of time the tap was opened before the sample to be
analyzed was collected. Site G was selected for this study because it was
the most distant in the distribution system and chlorine concentrations were
consistently lower there than at the other sites (See Table 22).
Table 28 summarizes the data obtained during these experiments. Note
that there was an increase in THM concentrations in samples collected after
the initial sample on both occasions. The extremely low CHC13 concentration
observed on June 8 (1 yg/1) was lower than any ever observed, and it was not
an error in the analysis. On June 15, the TTHM concentration in the initial
sample was less than one-half that in the next sample. Note that the
chlorine concentrations in the first sample collected on both days was zero
but reached its maximum rather quickly. The data indicate that some factor
may be reducing THM concentrations in the distribution system. This
possibility, as well as the factors related to chlorine dissipation, merits
further investigation.
Haloforms in Filter Back-Wash Water—
In June, 1977, four samples of back-wash water from the FCWA New Lorton
facility were collected and analyzed for volatile organics, TOC, and chlorine.
On two occasions, the water passing the filter immediately before and after
backwash were also collected for analysis. Table 29 shows the results of
these analyses.
It can be seen that the differences in haloform concentrations before,
after, and during backwash were all about the same in spite of the fact that
the TOC concentrations in the backwash water itself were 2.5 - 3.0 times as
74
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high as in the other samples. Of course, what is not known is how long the
chlorine persisted after the samples were collected, and it is possible
that the haloform reaction in the samples of backwash water were chlorine
limited. However, the nature of the organics may have been such that they
did not readily enter the haloform reaction.
The objective of the study was to determine if the water passing a filter
immediately before and after a filter had been disturbed by backwashing would
be more likely to contain higher concentrations of TOG and haloforms than at
other times. No significant differences were observed.
77
-------
REFERENCES
1. National Secondary Drinking Water Regulations— Proposed Regulations.
Federal Register, 42, No. 62, Thursday, March 31, 1977, pp. 17144-17146
2. National Interim Primary Drinking Water Regulations, EPA-570/9-76-003,
Office of Water Supply, U. S. Environmental Protection Agency, Washington,
D.C., 1976. 159 pp.
3. Helsel, D. R., Kim, J. I., Grizzard, T. J., Randall, C. W., and Hoehn,
R. C. Land Use Influences on Metal Yields in Storm Drainage. Journal
Water Pollution Control Federation, 51: 709, 1979.
4. Randall, C. W., Hensel, D. R., Grizzard, T. J., and Hoehn, R.C. The
Impact of Atmospheric Contaminants on Storm Water Quality in an Urban
Area. In: Progress in Water Technology— Proceedings of the 9th Inter-
national Conference of the International Association on Water Pollution
Research, Pergamon Press, Great Britain, 10:417, 1979.
5. McCabe, L. J., Symons, J. M., Lee, R. D., and Robeck, G. G. Survey of
Community Water Supply Systems. Journal American Water Works Association,
62: 670, 1970.
6. Drinking Water and Health. Safe Drinking Water Committee, Advisory Cen-
ter on Toxicology, Assembly of Life Sciences, National Research Council.
National Academy of Sciences, Washington, D. C., 1977. 939 pp.
7. Sanborn, J. T. The Fate of Select Pesticides in the Aquatic Environment.
EPA-660/3-74-025, National Environmental Research Center, U. S. Environ-
mental Protection Agency, Corvallis,Oregon, 83 pp.
8. Control of Organic Chemical Contaminants in Drinking Water, Environmental
Protection Agency Interim Primary Drinking Water Regulations, Federal
Register, 43, No. 28, Thursday, February 9, 1978, pp. 5756-5780.
9. Rook, J. J. Formation of Haloforms During Chlorination of Natural Waters.
Journal Water Treatment Examination, 23: 234-243, 1974.
10. Bellar, T. A., Lichtenberg, J. J., and Kroner, R. C. The Occurrence of
Organohalides in Chlorinated Drinking Water. Journal American Water Works
Association, 66(12): 703-706, 1974.
11. Stevens, A. A., Slocum, C. J., Seeger, D. R., Robeck, G. G. Chlorination
of Organics in Drinking Water. Journal American Water Works Association,
68(11): 615-620, 1976.
12. Symons, J. M., Bellar, T. A. Carswell, J. K., DeMarco, J., Kropp, K. L.,
Robeck, G. G., Seeger, D. R., Slocum, C. J., Smith, B. L., and Stevens,
A. A. National Organics Reconnaissance Survey for Halogenated Organics,
Journal American Water Works Association 67(1): 634-647, 1975.
78
-------
13. Hoehn, R. C., Randall, C. W., Fluegge, R. A., Shaffer, T.P.B., Taylor, P.,
Tanaka, C., Lichtenberg, J. J., and Bellar, T. A. An Evaluation of Purge-
Trap Procedures for Trihalomethane Analyses. In: Proceedings of the
Fifth Water Quality Technology Conference, American Water Works Associa-
tion, Kansas City, Missouri, November, 1977, Paper 3- A-2, 18 p. 1978.
14. Scheiman, N. A., Saunders, R. A., and Saallfeld, S. E. Organic Contami-
nants in the District of Columbia Water Supply, Journal of Biomedical
Mass Spectrometry, 1: 209-211, 1974.
15. Young, J. S., Jr., and Singer, P. C. Chloroform Formation in Public
Water Supplies: A Case Study. Journal American Water Works Association,
71(2): 87-94.
16. Wood, P. R. and DeMarco, J. Effectiveness of Various Adsorbents in
Removing Organic Compounds from Water. Part II. Removing Total Organic
Carbon and THM Precursor Substances. In: Activated Carbon Adsorption
of Organics from the Aqueous Phase, I. H. Suffet and M. J. McGuire, eds.
Ann Arbor Science Publishers, Inc., Ann Arbor, Michigan (In Press).
Presented at the 176th American Chemical Society Meeting, Miama, Florida,
September, 1978.
17. Lower Mississippi River Facility, Slidell, Louisiana Surveillance and
Analysis Division. New Orleans Area Water Supply Study— Draft Report,
EPA-906/10-74-002, U.S. Environmental Protection AGency, Region VI,
Dallas, Texas, 1974.
18. Thompson, B. C. Trihalomethane Formation Potential of Algal Extracellu-
lar Products and Biomass. M.S. Thesis, Virginia Polytechnic Institute
and State University, Blacksburg, Virginia, 1978. 123 pp.
19. Barnes, D. B. Trihalomethane-Forming Potential of Algal Extracellular
Products and Biomass. M.S. Thesis, Virginia Polytechnic Institute and
State University, Blacksburg, Virginia/ 1978. 169 pp.
20. Morris, J. C. Formation of Halogenated Organics by Chlorination of Water
Supplies. EPA-600/1-75-002, U.S. Environmental Protection AGency,
Washington, D.C., 1975. 54 pp.
21. Hoehn, R. C., Goode, R. P., Randall, C. W., and Shaffer, P.T.B. Chlori-
nation and Water Treatment for Minimizing Trihalomethanes in Drinking
Water. In: Water Chlorination: Environmental Impact and Health Effects,
Volume 2, R. A. Jolley, ed. Ann Arbor Science Publishers, Ann Arbor,
Michigan, 1978, pp. 519-535.
22. Environmental Protection Agency, Algal Assay Procedure: Bottle Test,
National Eutrophication Research Program (Eutrophication and Lake
Restoration Branch), National Environmental Research Center, Corvallis,
Oregon. August, 1971.
79
-------
SUPPLEMENTAL DATA
The contract required that with each sampling, supplemental data—
including pH, chlorine residuals, bacterial counts, weather conditions, and
notes concerning any unusual water-quality characteristics— be collected
and compiled. The data appear in Appendix D. Table D-l includes information
related to virus monitoring, another aspect of the contract not covered by
this report, but Table D-2 contains supplemental data relative only to the
volatile organics sampling program.
80
-------
APPENDIX A
Heavy Metal Concentrations At Sites A
Through F for the Period
June, 1975 - May, 1976
81
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Volatile Organics Concentrations
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TABLE C-5. BIHOURLY VARIATIONS IN THE CONCENTRATIONS (MICROGRAMS PER LITER)
OF HALOGENATED METHANES OBSERVED IN RAW WATER (SITE C) AND FINISHED WATER
AT THE FAIRFAX COUNTY WATER AUTHORITY'S WATER TREATMENT PLANT
(SITE D). SEPTEMBER 11, 1975
Site C
Time CHC1,
2400 3
0210 2
0410 <1
0610 <1
0810 <1
1010 <1
1200
1410 <1
1610 2
1805 3
2000 5
2215 <1
2400 <1
***
Mean 1.3
Standard
Deviation 1.7
Range 0-5
Time
2400
0200
0400
0600
0810
1000
1200
1400
1600
1800
**
2000
2200
2400
***
Mean
Standard
Deviation
Range
Site D
CHC13
418
445
345
337
390
398
376
392
378
384
378
413
367
386.2
29.0
337-445
CHCl2Br
26
19
17
29
19
19
21
21
22
17
24
23
21
21.4
3.5
17-29
**
***
Dichlorobromomethane (CHBrCl-) concentration all <1
1 tig/1 dibromochlorotaethane, CHClBr., was found also at this ti
Site D.
Values <1 considered 0 uoan calculating mean
.me at
112
-------
TABLE C-6. BIHOURLY VARIATIONS IN THE CONCENTRATIONS OF HALOGENATED
METHANES (MICROGRAMS PER LITER) OBSERVED IN TWO DISTRIBUTION
SYSTEM SITES: FAIRFAX COUNTY WATER AUTHORITY'S STORAGE
YARD (SITE E) AND IN ALEXANDRIA, VIRGINIA (SITE F) ON
SEPTEMBER 11. 1975
T-tmn
2400
0200
0400
0600
0800
1000
1200
1400
1600*
1800
2000
2200
2400
Mean**
SITE E
CHC13
363
447
419
400
379
382
404
352
379
398
410
405
390
394.5
CHCl2Br
22
25
23
24
23
22
25
27
22
23
22
23
20
23.2
CHC13
256
404
391
404
423
373
345
413
236
314
342
332
298
Mean** 348.5
SITE F
CHCl2Br
16
22
23
20
23
18
14
21
14
17
18
19
20
18.9
CHClBr2
<1
2
1
2
1
10
6
6
6
2
3
<1
6
3.5
Standard
Deviation 24.7 1.8
Range 352-447 20-27
Standard
Deviation 60.3
Range
236-423
3.1 3.0
14-23 0-10
At Site F, 1 yg/1 bromoform, CHBr_, was found also at this time.
**
Values <1 considered 0 when calculating mean
113
-------
TABLE C-7. CONCENTRATIONS >1 yg/1 DIBROMOCHLOROMETHANE AND 1, 2-DICHLORO-
ETHANE + CARBON TETRACHLQRIDE* OBSERVED AT VARIOUS SITES. WITHIN THE
OCCOQUAN WATERSHED AND WATER SERVICE AREA, JUNE 1975-MAY 1976
COMPOUND SITE DATE OBSERVED CONCENTRATION, yg/1
CHClBr2 D August 25 1
September 1 1
September 11 1
November 10 2
E August 18 1
October 8 2
F June 30 1
July 7 1
August 4 5
August 18 1
August 25 1
September 1 1
September 11 (See Table C-6)
October 6 2
October 8 3
November 10 6
1, 2-DCE* A June 17 10
+ June 24 4
CC1, September 11 1
October 7 2
B June 10 4
June 24 3
July 1 3
September 11 1
October 7 4
C June 9 1
June 16 1
June 28 1
D June 9 34
Separation not attained
114
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APPENDIX D
Supplemental Data Collected on. Each. Sampling
Date During the Monitoring Program
Key to Table Abbreviations;
OCP - Organochlorine Pesticides
OPI = Organophosphorus Insecticides
CPH = Chlorophenoxy Herbicides
VO - Volatile Organics
HM = Heavy Metals
MPN = Most Probable Number of Coliforms per 100 ml
TPC = Standard Total Plate Count per ml
Key to Observations (Last Column);
1 » Low Turbidity,-No Unusual Odor or Color
2 = Moderate Turbidity; No Unusual Odor or Color
3 = High Turbidity; No Unusual Odor or Color
4 = Clear, Colorless, No Unusual Odor
Key to Sites:
A = Catharpin, Upper Bull Run Above Treated Sewage Discharges
B = Bull Run Below Treated Sewage Discharges
C = Intake Water at the Fairfax County Water Authority's Water
Treatment Facility
D = Finished Water at the Fairfax County Water Authority's Water
Treatment Facility
E = Distribution System at the Fairfax County Water Authority's
Storage Yard
F = Distribution System in Alexandira, Virginia
G = Distribution System in Dumfries, Virginia
133
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162
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APPENDIX E
RESULTS OF THE MULTIPLE REGRESSION ANALYSIS
OF RAW WATER CHARACTERISTICS AND TRIHALOMETHANE CONCENTRATIONS
163
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APPENDIX E
RESULTS OF THE MULTIPLE REGRESSION ANALYSIS OF RAW WATER
CHARACTERISTICS AND THM CONCENTRATIONS
The multiple regression analysis reduced the number of significant
independent values to four or less, giving best-fit relationships of the
form:
TTHM - a + bx., + b%2 + ex-... [3]
The best-fit relationships developed with variables for which there were
from 16 to 19 observations are summarized as follows:
TTHM - -20.13 + 0.007 DO + 0.129 Rain + 0.160 Stage
s
+ 0.197 Cl2-Appl- [4]
TTHM - -16.63 + .005 DO + 0.123 Rain + 0.136 Stage
S
+ 0.178 Cl2-Dem [5]
TTHM . -0.56 + 0.007 DO + 0.122 Rain
s
+ 0.182 Cl2-Dem [6]
Where:
TTHM » total trihalomethanes
D0_ a surface dissolved oxygen concentration, percent saturation
S
Rain » rainfall, in./mo.
Cl.-Appl " total chlorine applied during treatment, mg/1
Cl2-Dem " chlorine demand (total applied - total residual), mg/1
Stage » reservoir stage, ft. (maximum = 120)
Next, the analysis was applied to data for which there were 35 observa-
tions for all parameters. The resulting equations were:
TTHM - 1.61 + 0.09 Rain - 0.056 Turb - 0.020 Color
- 0.562 Cl2-Appl + 0.600 Cl2~Dem [7]
164
-------
TTHM = 1.46 - 0.057 Turb - 0.023 Color
- 0.537 Cl2-Appl + 0.621 Cl^Den. [8]
TTHM - 1.21 + 0.100 Rain - 0.450 Cl -Appl
+ 0.582 Cl2-Dem [9]
Where:
Color = standard color units
Turb - turbidity, JTU
When chlorine data were omitted, the correlation coefficients were much lower.
A summary of the statistics generated by the analyses represented by equations
[4] - [9] is presented in Table E-l.
A comprehensive discussion of the meaning of terms displayed in Table E-l
is beyond the scope of intent for this report, but a few comments will be made
to help interpret the significance of the statistical data presented there:
2 2
1. R : The closer R is to 1.00, the better the variables fit the
regression equation.
2. MSE: "Mean square error" (MSB) statistic related to the "Sum of
squares error"(SSE)in that it is calculated by dividing SSE
by the degrees of freedom (number of observations minus
number of parameters in the equation minus 1.0). The lower
the MSE, the better the indication is that the regression
equation describes the true conditions that explain the
TTHM variations.
3. SSE: Is that portion of the total sum of squares of the dependent
variables (TTHM concentrations squared, in this analysis)
which is not accounted for by the "model" but, instead, is
due to random errors in measurements, to random variations
in the variables themselves, or to unknown factors which
were not included in the model. The lower the SSE, the
better the equation describes the true conditions that
explain the TTHM variations.
4. Press: The "press statistic" results from an analysis in which the
variables are removed one at a time and the ability of the
regression equation to "predict" that known variable's
165
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TABLE fi-1. STATISTICS ASSOCIATED WITH MULTIPLE REGRESSION ANALYSES
OF TRIHALOMETHANES AND WATER-QUALITY DATA
Equation
[4]
[5]
[6]
[7]
[8]
[9]
Observations
16
18
16
18
16
19
35
35
35
R2
0.914
0.910
0.910
0.893
0.888
0.873
0.771
0.738
0.684
* ,*
UO17 OOT?
^lOIZi &d£i
0.084 1.550
0.093
0.094 1.550
0.111
0.100 1.846
0.123
0.219 6.36
0.242 7.27
0.283 8.77
^P.-ess
3.019
3.045
3.314
10.68
10.21
11.86
Mean Square Error
Sum of Squares Error
Press Statistic. See text for discussion.
166
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value Is assessed. The process is repeated until all data
have been removed and replaced. The value of the press
statistic, if low and similar to the value of the SSE,
indicates that the data not only are well-described by the
2
regression equation (if R is high) but also that the
equation is a good predictor of TTHM values. In other words,
a good "model" has been developed.
A summary interpretation of the multiple regression analyses, as indicated by
their statistics in Table E-l is as follows: Equations [4], [5], and [6]
provided reasonably good descriptions of the data, but there simply were too
few analyses to adjudge those as "good models." The increase in the number
2
of observations caused the R values to decrease, and the Press Statistics
were higher than the SSZ terms.
167
"S-U. S. GOVERNMENT PRINTING OFFICE: 1979 -281-147/139
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